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GEOS 260 > General > Flashcards

General Flashcards

1
Q
A
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2
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3
Q

2V angle.

A

This is the acute angle between the two OAs within biaxial minerals.

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4
Q

4 symmetry elements

A

Inversion: This is where an element is shown on the equal but opposite face. It is reflection through the crystal center not a plane.

Reflection: This is the planar reflection of elements.

Rotation: This is a repeating motif that is rotated about an axis.

Rotoinversion: When there is a shift and inversion in a regular pattern.

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5
Q

4 types of twinning

A

Contact twins: Rotational symmetry/mirror plane down a central axis. Both sides of the plane are the exact same but this symmetry does not normally occur in the mineral.

Interpenetrant: two or more crystals growing near each other and impending on the others growth. It is defined by a twin axis.

Polysynthetic: twins growing parallel to one another in a repeating set. Plagioclase.

Cyclical: repeated twinning of 3 or more crystals with a non-parallel twin axis. It is like polysynthetic but instead of mirrors the crystals are rotated about a central axis.

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6
Q

Acute Bisetrix Figure (BXA)

A

This is when the two isogyres form arcs or uneven arcs. The distance between the isogyres is proportional to the 2V between the OAs by the degree of seperation where 50o is just at the edge of view.

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7
Q

Acute Bisetrix Figure (BXA)

A

Starting at 45 degrees off of extinction at the far left and then rotating 45 degrees.

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8
Q

allochromatic

A

This is when transition metals occur as trace elements to color a gem. This means that the coloring agent is an impurity and it is “other colored”

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9
Q

almadine spectra

A

The high and low ends fade out and there is a significant chunk of yellow missing.

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10
Q

Amorphous expected results from the refractometer

A

It should be singly refractive and have a single, fixed shadow edge.

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11
Q

Amorphous

A

These are non-crystalline solids that do not have regularity in their mineral composition.

Metamict minerals are minerals that lose their crystallization due to radiation.

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12
Q

Anisotropic Minerals

A

Minerals that have vector dependent physical properties. Particularily concerning a change in the speed of light based on the light direction.

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13
Q

Anomalous Double Refraction

A

This is when a gem that is otherwise isotropic experiences strain to create zones, patches, or lines of anisotropism.

Be sure to rotate the gem to ensure that it is not the result of coloring or faceting. Focus on one spot and rotate the gem several times to ensure that it is anomalous extinction.

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14
Q

Anomalous Double Refraction

A

This is when a crystal is strained so only parts go extinct in the polariscope, NOT the full crystal.

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15
Q

Artificial Materials

A

These are materials that have been exclusively manufactured. They are not natural

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16
Q

Asterism examples

A

Corundum, almandine, quartz, diopside

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17
Q

BARS

A

This stands for a bunch of very long Russian names. It is very similar to the belt but it uses cyclindric anvils and an octohedral cell to form the diamond.

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18
Q

Biaxial Interference Figures

A
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19
Q

Biaxial/Uniaxial Positive vs. Negative

A

This is a term referring to whether the OAs are closer to the minimum refractive plane or the maximum. Positive minerals have OA closer to the maximum.

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20
Q

Biaxial systems and materials

A

These are characterized by 3 refractive indices (two varying RI’s) and 2 OA’s. The middle “n” can then be further used to designate positive or negative which is related to the crystallographic axes.

The ‘ic’ systems:

Orthorhombic, monoclinic, triclinic

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21
Q

Uniaxial Indicatrix

A

This is the spheroid that is derived for the uniaxial e and o ray. Because uniaxial minerals do NOT have a mid-axis there is variation between the maximum refractive index (epsilon) and the minimum (little omega).

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22
Q

Bleaching

A

This is the use of chemicals or other agents to lighten or remove the color of a gemstone. Common stones that are bleached include pearl (kills bacteria), coral, jadeite, tiger’s eye, other quartz.

It needs to be treated with caution because it can lower the durability of a stone.

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23
Q

Bonding types of:

Halides, Oxides, Silicates, Sulfides, and sulfosalts

A

Halides: Primarily ionic

Oxides: ~75% ionic (corondum)

Silicates: Range from ~50% to ~25% ionic based on network

Sulfides: ~65% covalent and becomes more metallic with increased electron shells

Sulfosalts: ~40% metallic (stibnite)

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24
Q

Braveno Law

A

This is a polysynthetic twin along the {021} plane in orthoclase. This means that it is parallel to the a axis b intersects b:c at a 2:1 ratio (it is diagonal). It is common in orthoclase.

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25
Q

Carbonate Gems

A

M+x

These are very soft and non-resilient

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26
Q

Carlsbad Law

A

This is a penetration twin that shows 180o rotation about the [001] axis. It is characteristic of orthoclase.

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27
Q

Diamond Testing: Cathodoluminescence

A

Cathodeluminescence is using a beam of electrons to create excitation within an atom. It is used in diamond to identify the growth patterns

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28
Q

Cause of Chatoyancy/Asterism

A

These are reflections perpendicular to long acicular needles within stones that are oriented parallel to one another.

It is only obvious when cut as a cabachon. It can only be seen when the light is perpendicular to the stone.

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29
Q

Centipede inclusions

A

This occurs in moonstone and it looks like elongated snowflakes.

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30
Q

Ceramics imitation

A

These are used to produce “synthetic” turquoise, lapis lazuli, and coral using a sintering process to solidify a powdered material.

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31
Q

Character of oxide gems

A

Fundamentally [M+]Ox

High hardness and resistance to injury/chemical attack

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32
Q

Characteristic Spectroscope Results

A

Emission lines: Ruby has a red emission line and green is missing

Sharp lines: REE’s

Fe: cut off of red, missing yellow

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33
Q

Chatoyant Stones

A

Chrysoberyl, quartz, tourmaline, glass with optical fibers

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34
Q

Choice of Cut Factors (8)

A

Yield: maximized

Transparency: Transparent stones are faceted, translucent and opaque stones are cut as cabochons, beds, carvings, or inlay

Fire and Brilliance: Facets maximize the best dispersion

Inclusions: Some cuts highlight inclusions other hide.

Optical Effects: Usually with cabochons (chatoyancy)

Color: Maximize attractiveness and utilize pleochroic properties (tourmaline)

Physical constraints: Cleavage, anisotropic hardness, durability

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35
Q

Chromium Coloring examples and effects

A

Ruby: red, emerald: green, green jadeite jade: bright green, alexandrite: red/green, red spinel

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36
Q

Cleavage

A

This is defined as the plane of weakest atomic bonding. It is a sub-set of fracturing and is dependent of the crystal system and structure.

It is very important for cutting and faceting gems.

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37
Q

Cleavage examples

A

none: obsidian, quartz (fracture)

2 directions: orthoclase, amphibole

3: galena (90o), calcite (105, 75)
4: Fluorite

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38
Q

Coating

A

This is the application of a colored layer to change or improve the colour of the gem. This commonly includes quartz, topaz, cubic zirconia, and diamonds.

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39
Q

Coating ID

A

They durability of various coatings is variable and on older stones they may begin to curl or flake particularly along facet edges.

Looking at the back of the stone can show the film’s iridescence and the spectrum is likely influenced of the coating and not of the stone. It will be abnormal.

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40
Q

Color change stones

A

This occurs in corundum, spinel, garnet, fluorite, and zircon.

Of note is alexandrite that rarely shows color change and is very desirable.

Color change is the optical phenomena where stones change color based on the light source. Most commonly this is either incandescent (tungsten bulbs) and sunlight

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41
Q

Color in gemstones is a function of…

A

The source of white light, modifications to said light, and the eye/brain’s interpretation of the light.

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42
Q

Color Zoning

A

This includes structural related coloration of stones due to different trace or transition elements.

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43
Q

Common forms of Corundum?

A

Corundum is trigonal and will have triangles on the upper face if tabular or will be bipyramidal or barrel shaped.

All forms have a tendency to have striations on the sides and hexagonal color zoning.

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44
Q

Common nomenclature changes

(Spessartine, zoisite, beryl, Corundum, Cordierite)

A

mineral = gem

Spessartine = spessartite

zoisite = tanzanite

beryl = emerald

Corundum = Sapphire/Ruby

Cordierite = Iolite

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45
Q

Common Volcanic Rock Textures

A

Vesicular Textures: There are “bubble formations” due to off-gassing of relatively low-gas lava

Pyroclastic: These include the explosive debris of volcanic eruptions.

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46
Q

Composite gem Materials

A

These are materials that composed of two (doublets) or three (triplets) stones/pieces.

They are generally plates of material acting as backing or on the surface providing a false front.

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47
Q

Composite Materials

A

These are artificially assembled from two or more natural or artificial components meant to replicate a single gem material.

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48
Q

Conoscope

A

This is a glass ball that is used to find interference figures, which occur along the c axis of the stone, from a material in the polariscope. Used to identify if the anisotropic/doubly refractive stone is uniaxial or biaxial.

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49
Q

Conoscope Use

A

When rotating the stone in polarized light look for interference colors (iridescence). When noted touch the conoscope to that part of the stone and look to see if the stone is uniaxial or biaxial.

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50
Q

Coordination Number

A

The total number of atoms surrounding a central cation in a molecule

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51
Q

Coral Types

A

Red Coral: Classic Mediterranean coral that is very pricey

Black Coral: Hawaiian coral. It always has bumps/dots. Also pricey. Caribbean black coral is a psuedo-simulant that is worth about 100x less.

Golden Corals: These are deepwater corals often dyed

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52
Q

Corundum Diffusion

A

Heating pink sapphires in the presence of beryllium shifts their color to orange. Similar processes with various other small radii elements fill vacancies and create other colors. This can leave a rind of low diffusion/high conentration.

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53
Q

Criterion for judging a faceted stone

A

Look at the symmetry, proportions, and polish

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54
Q

Critical angle for total internal reflection

A

This is ic and it represents when the refracted ray is at the interface of the two materials so r=90o it occurs at sin-1(nr/ni) where n is the refractive index

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55
Q

Crown angle

A

This is the angle between horizontal and the area below the girdle, it determines dispersion. If it is over 42o then you can see straight through the diamond (lack of dispersion) and if it is less than 42o then the girdle is refelcted to create a “fish eye”

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56
Q

Crystal Aggregation Habits and examples

(7 kinds)

A

Granular: Like marble or granite

Lamellar/foliated/micaceous: mica

colloform/stalactitic: cave deposits

geode

oolitic: iron ore
radiating: wavellite

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57
Q

Crystal Habit and 14 Types

A

This is how minerals display crystal faces dependent upon their growth environment. It is described by the general shape of the crystal.

Types:

Acicular: slender needles

Bipyramidal

Botryoidal or globular: Hemispherical masses

Columnar or Fibrous: series of slender prisms

Dendritic

Dodecahedral

Euhedral

Mamillary: rounded intersecting contours

Massive: lacks crystal shape

Octohedral

Prismatic: Collumnar, there is a substantial thickness to the collumns

scalenohedron: A six-sided pyramid with unequal sides

Striations: Growth lines of the crystal face.

Tabular: short stubby crystals

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58
Q

Crystal Pulling

A

This is a method used to produce laser grade corundum, chrysoberyl, YAG (yitrium aluminum garnet), and GGG.

The idea is that there is a tub of melted solution and a seed crystal is placed at the surface where it nucleates a crystal. This is very slowly pulled upwards to form a boule.

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59
Q

Crystallization from a melt

A

This is the concept of having molten materials that are slowly cooled to form a crystal. This includes the Verneuil flame-fusion, zone melting, crystal pulling, and skull melting processes.

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60
Q

Crystallization from a solution.

A

This involves having either a flux or hydrothermal solution that enables the reactents to be dissolved. This is then perturbed into instability (primarily by lowering P/T) to promote crystallization.

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61
Q

Cubic Zirconia vs. Zircon UV reaction

A

SWUV: zirconia is yellow to dull orange. zircon is inert

LWUV: same, slightly weaker. Zircon is brown-yellow

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62
Q

Cubic/Isometric system and gem examples

A

a=b=c and meet at 90o

Displays the highest degree of symmetry (three four fold rotational, four three fold, 4 mirror planes)

Gems: Diamond, fluorite, garnet, spinel, pyrite

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63
Q

Cutters

A

These are workers who transform a rough stone into the mold for a gem.

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64
Q

CVD synthetic diamonds

A

Chemical vapour deposition growth practically forms polysynthetic diamonds by punping inert gases and diamonds gas into a chamber

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65
Q

Desirability

A

Customer must want the stone for some reason. Commonly this includes

Want to be appreciated by others (gifts)

Fashions/seasons

Social customs: birthstones, royalty/celebrity

Myths and Legends: Metaphysics

Ethical considerations

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66
Q

Anisotropic hardness

A

All crystals can show directional hardness although it is less obvious among some species, kyanite is one of the most obvious.

Note: Diamonds’s anisotropy is why it is able to be polished.

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67
Q

Diamond Fluorescence

A

SWUV: generally weak

LWUV: variable, oftentimes blue

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68
Q

Diamond grading

A

There are independent scales for color and clarity that are subjectively graded.

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69
Q

Diamond Manufacture

A

This is the process of fashioning and polishing a diamond

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70
Q

Diamond ore mineral processing

A

Ore is usually put into a SAG mill and can be sorted using x-ray fluorescence or because they are non-polar they stick to a grease covered belt.

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71
Q

Diamond Types

A

Generally diamond types are a function of impurities and vacancies that give them semi-diagnostic properties.

type 1 diamonds deal with nitrogen

type 2 diamonds do not have nitrogen

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72
Q

Diamond View (De Beers unit)

A

This uses UV fluorescence to identify diamond types

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73
Q

Diamonds: Black

A

These are either the result of numerous inclusions (Carbon), treatment, or extremely high concentrations of nitrogen.

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74
Q

Diamonds: Brown

A

This is due to the plastic deformation of diamonds that causes a unit step shift and unalignment of the atoms. It occurs in high shear enviroments.

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75
Q

Diamonds: Green

A

This is from radiation defects creating lattice vacancies that emit green light upon excitation.

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76
Q

Diamonds: Orange

A

This is the collusion of nitrogen, hydrogen, and nickel.

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77
Q

Diamonds: Pink

A

These are thought to be colored due to deformation and only come from the Argyle Mine in Australia. Some are thought to have manganese impurities.

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78
Q

Diamonds: Type I

A

This is when there are nitrogen atoms dispersed throughout the structure. It produces a “Canary Yellow” color.

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79
Q

Diamonds: Type IIb

A

These diamonds contain boron which allows them to conduct electricity and create a blue to blue-grey coloration.

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80
Q

Dichroscope

A

This is a loupe with two polarizers in opposite directions that enable a person to have the stone’s pleochroic character exemplified.

Stones must be colored and doubly refractive.

Report resulting colors and intensity. (trichroism is only seen in biaxial materials)

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81
Q

Different kinds of lustre

A

Adamantine (diamond only)

Sub adamantine: zircon

Bright vitreous: Corundum

vitreous: glass

Dull vitreous: malachite

Resinous: Amber

Waxy: turquoise

Metallic: hematite

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82
Q

Differentiating synthetic and natural opal

A

Synthetic opal tends to have a collumnar structure and polygons of light reflection it is also more porous and does not phosphoresces green like most natural opals after exposed to LWUV

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83
Q

Disclosure and regulation groups/guidelines

A

CIBJO helps to advise and provide a confederation of similarily interested individuals, organizations, and companies

FTC has a jewelry guide about how to properly label gems and jewelry

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84
Q

Does glass fluoresce in LWUV?

A

Glass only fluoresces in SWUV

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85
Q

Double Refraction

A

This describes all anisotropic (biaxial) materials where an incident ray is split into more than one ray upon entering the material. This is the reason for “doubling” of images, like optical calcite.

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86
Q

Durability

A

This is a term that relates to a gems ability to resist change due to light, acid, oil, or heat, (stability), the hardness, and the toughness of the gem.

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87
Q

Dyeing

A

This can be done on any permeable material and involves soaking a material in a liquid to improve the color consistency throughout a stone.

It is common to do after bleaching

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88
Q

Dyeing ID

A

look for sharp changes in color in cracks/veins. The absorption spectrum of the material will match to dye and not the stone itself. They may also show discrete patches of fluorescence/non-flourescence.

Acetone test: DESTRUCTIVE use with caution but a swab with acetone will stain most organic dyes

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89
Q

ED-XRF

A

This is an energy dispersive x-ray fluorescence spectrometer.

It is a non-destructive quantitative bulk chemical analysis technique with the limitation that it can only detect heavier elements meaning those with higher atomic numbers.

Pearls: Detects Mn in freshwater pearls and Sr in saltwater pearls. Cannot seperate natural and cultured pearls

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90
Q

Elongated gas bubbles and swirls inclusion

A

These are long squirly inclusions that are indicative of glass.

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91
Q

Emission lines and fluorescence

A

An emission line in a spectrum will appear as a high energy peak in a plot of Intensity vs. wavelength

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92
Q

enantiomorph

A

A crystal which has a mirror image habits and optical characteristics occurring both in right and left handed forms.

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93
Q

Examples of carbonate gems

A

Calcite CaCO3

Malachite Cu2(OH)2CO3

Rhodochrosite MnCO3

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94
Q

Examples of crystal habits

A

Acicular: rutilated quartz

Bipyrimidal: Sapphires

Botryoidal/globular: chalcedony or hematite

columnar/fibrous: kyanite, calcite

dendritic: moss agate
dodecahedral: garnet
euhedral: diamond, spinel, quartz

Mamillary: malachite

massive: rose quartz
octohedral: diamond, spinel
prismatic: tourmaline, quartz, zircon
scelenohedron: Sapphire

Striations: tourmaline, quartz, pyrites

Tabular: Ruby

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95
Q

Examples of cyclosilicate gems

A

Beryl (aquamarine), benitoite, cordierite, tourmaline

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96
Q

Examples of Framework Silicate Gems

A

Feldspar, Sodalite

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97
Q

Examples of Inosilicate Gems

A

Single-Chain (pyroxenes): Jade, rhodonite

Double chain: Amphiboles

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98
Q

Examples of Neso Silicate Gems

A

Olivine, Garnets, the aluminosilicate series (sillimanite, andalusite, and kyanite), topaz, zircon, staurolite

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99
Q

Examples of sheet/phyllosilicate gems

A

Micas, Chlorite

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100
Q

Examples of Sorosilicate Gems

A

Zoisite (Epidote), Vesuvianite (Idocrase)

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101
Q

Expected results from a hexagonal crystal in the refractometer

A

There would be two shadow edges but only one moves. This shows it is double refractive and uniaxial.

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102
Q

Facet terms (table, cutlet, girdle, crown)

A

The table is the top of the facet.

The girdle is the vertical band around the stone’s midsection that is used to keep the stone in its setting

The cutlet is a little flat part at the bottom tip of the stone that helps prevent brittle fractures and reduces cut imperfections.

The crown is the part of the stone above the girdle.

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103
Q

Feathers

A

This is a type of inclusion that represents a “healed” fracture. It looks like a fracture but it is not a plane that has cohesion it is generally less sharp.

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104
Q

Ferrous vs ferric coloring

A

Ferrous (Fe2+) causes the green of peridot and red of almandine

Ferric iron (Fe3+) causes the green color in sapphire

Iron is also responsible for the blue colors of aquamarine and blue spinel

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105
Q

Fluorescence

A

This is the emission of visible light due to excitation of atoms due to higher energy light interference. It is caused by short wavelength light (E=k(1/lambda))

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106
Q

Flux-Melt Technique

A

This is used for emerald, ruby, sapphire, spinel, and alexandrite

It has a series of strung seed crystals in a platinum container with different reactants above and below the seed crystals and a flux in the center. This is heated so the reactants go into solution and precipitate onto the seed crystals.

This is identified by the presence of “wispy veils” not “fingerprints” in emeralds and corondum

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107
Q

Color Terms (4 types)

A

Hue: secondary vs. primary (eg Purplish-blue)

Tone: Light or dark (eg light blue)

Saturation: Color intensity; deep, bright, vivid, pale

Consistency of Color: Even, patchy, zoned, bi-colored, parti-colored

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108
Q

Four types of cleavage

A

Basal: Parallel to the pinacoid. 1 direction of cleavage.

Octohedral: Parallel to octohedral faces (flourite, grows cubic)

Prismatic: Parallel to prism faces. This has four directions of cleavage.

Rhombohedral: Parallel to the rhomb faces (calcite). This is three directions of cleavage.

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109
Q

Fracture

A

This is an inclusion that represents a random, non-directional break within a stone.

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110
Q

Fracture and 4 types

A

This is a broad category that primarily describes how something breaks that is not on a cleavage plane.

It is conchoidal, hackly, splintery, or smooth (diamonds)

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111
Q

Fracture examples:

A

conchoidial: quartz, obsidian
hackly: gold, silver, platinum
splintery: kyanite, serpentine
uneven: ammolite, chrysocolla

Granular: jade, jadeite, lapis lazuli

smooth/even: Basal topaz

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112
Q

Fracture Filling

A

This is the filling process that involves filling fractures with polymers or oils to remove the optical effects and improve durability.

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113
Q

Fracture Filling Diamond

A

This is done through using a high RI glass. Look for a characteristic color flash (pink to green) and occasionally frisbee like bubbles form in the cracks.

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114
Q

Fracture Filling ID

A

Look for discrete planes of blue-yellow iridescence and bubbles/clouds (epoxy)

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115
Q

FTIR

A

Fourier transform infrared spectrometer

This is useful to identify diamond types, synthetic quartz, turquoise stabilization, and emerald determinations.

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116
Q

Fundamental Particles (Atom, proton, electron, neutron)

A

Atom: This is the smallest unit of ordinary matter that forms a chemical element. It is composed of particles.

Proton: Positive particles within an atom

Electron: Negative particles within an atom

Neutron: ~same mass as a proton but without an electric charge

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117
Q

Gel Growth

A

This is the process involved with producing “synthetic” opal (truly a simulent).

It involves suspending a gel of silica spherules that slowly settle and produce the simulent.

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118
Q

Gem mining

A

This is broken into

coloured stone mining: ASM (Myanmar, Brazil, Sri Lanka, and Madagascgar)

and Diamonds: LSM (Canada and Russia) divided by kimberlites and lamprolites

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119
Q

Gem Science/Gemology

A

The study of gems from origin to jewelry, including the study and identification of gemstones and their treatments.

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120
Q

Gem Simulant

A

This refers to when a gem substitute does not have the same structure as the original gem.

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121
Q

Gem Value

A

Cost Vs. Demand

Durability, rarity, beauty at time=t

properly identified and treatments considered.

4 C’s: Cut, Carat weight, Color, Clarity

5th C: Cost

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122
Q

Gems

A

Any material that is used for adornment or decoration especially when cut nad polished.

This includes rough or cut minerals chosen for their beauty and durability that have been cut and polished specifically for adornment. It also includes ornamental rock, biogenic/organic material, or artificial/synthetic.

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123
Q

Gemstone dealers

A

This is the group that sells the cut and polished stones to jewelersand retailers

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124
Q

Gemstone Pipeline

A

Generally the gemstones start at the production (mining or synthetic).

  1. ) they are traded between rough dealers, cutters, and treaters
  2. ) they are traded between cut dealers and manufacturers
  3. ) retail
  4. ) customer
  5. ) secondary market/auctions
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125
Q

Gemstone Treatment

A

This refers to a suite of potential alterations that is defined as the process of artificially altering and improving the appearance or properties of gem materials.

It ought to be disclosed by sellers.

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126
Q

General Cutting Procedure for a faceted diamond

A

Generally, you cut off the upper point. Then it is Butted which is rounding the stone. Then it is Faceted which gives the stone a few rough faces. This is finished by Brillianteering which includes adding all of the small faces and polishing.

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127
Q

Geologic Laws

A

Law of original horizontality: Rocks have a tendency to be created in horizontal layers

Law of Superposition: Older rocks have a tendency to be at the base of the formation under review.

Law of inclusions: This says that xenoliths/clasts are older than the layer they are found within.

Cross-Cutting: To be cross-cut the layer has to be older than the intrusion.

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128
Q

Hardness and Luster Relation

A

Harder gems are less likely to lose lust after being polished and will polish better.

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129
Q

Hardness

A

The ability of a material to resist scratching and abrasion, measured on the Moh’s scale of hardness. Look at how sharp the facets are and how deep scratches are to indicate relative hardness of a stone.

Hardness testing is destructive so always work from soft to hard testing in places that are not readily visible. Do not use a diamond point for testing.

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130
Q

heat treatment: amber

A

Heat treated amber removes the impurities and clouds in the stone but can leave a burnt crust on the edges and stress spangles.

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131
Q

Heat treatment: Corundum Other

A

At a variety of temperatures it can enhance color, remove inclusions, create inclusions, remove color, and create/remove chatoyancy.

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132
Q

Heat Treatments

A

This is a suite of treatments most commonly used to remove or even out color through changing the valency of transition metals, diffusing materials, or dehydration. It is also used to exsolve or dissolve inclusions (rutile in qtz). It can also be used to create fractures to mimic natural stones or increase the effects of dye.

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133
Q

Heating and Diffusion

A

This is used to improve the color of the stone and involves the reaction of various inclusions and elements within a stone changing valency or bonding.

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134
Q

Heating and Diffusion: Corundum

A

In the dark blue sapphires heating shifts Fe2+ to Fe3+ + e- This lightens the stone.

In Light blue sapphire there is low ferrous iron and potentially Ti4+ which creates a reducing enviroment to produce more ferrous iron and enhancing the blue color.

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135
Q

Heating and Irridation

A

This is the idea that heating causes valency shifts that can be reversed through irradiation. This includes beryl, quartz, and topaz

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136
Q

Heating and Irridation: Beryl

A

Aquamarine can be heated to become more blue by reducing beryllium and irridated to oxidize beryllium to form yellow helidor.

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137
Q

Heating and Irridation: Diamond

A

Various irridation at different temperatures can create carbon vacancies, transform carbon to nitrogen, and create nitrogen isotopes that produce distinctive spectra trackable with raman.

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138
Q

hexagonal crystal system, symmetry, and gem examples

A

This system has 6 equal faces parallel to the z-axis making it have 6 fold symmetry.

a=b/=c

α= 120o

β= γ= 90o

This is also said as having 4 axis (three in the x-y plane at 120 degrees and a z axis)

Gem Examples: Beryl (heliodor, aquamarines, morganite, emerald), apatite, taaffeite

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139
Q

Hexagonal and trigonal twinning

A

Contact twins (calcite)

Brazil and dauphine twins (qtz interpenetration twins)

Japan (qtz contact twin)

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140
Q

High Pressure High Temperature (HPHT_

A

This was developed in the 1950’s for diamonds and principally using a triaxial compression machine to compress a heated vessel of carbon to produce diamonds.

They two main machines are called the belt and BARS

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141
Q

horsetail/ponytail inclusions

A

These are radiating fibers that nucleate from one spot within demantoid garnets.

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142
Q

How is fossil ivory regulated?

A

Many states have legislation that limits the transport of ivory and fossil ivory across state bounds making it illegal to purchase unless a state resident.

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143
Q

How to find interference figures.

A

Rotate the stone until iridescence is seen

Orient the conoscope over this iridescence to see the interference figure.

144
Q

HPHT diamond coulours/types

A

This produces yellow to brownish yellow, type Ib

yellow diamonds

Blue diamonds Type IIb + Type Ib

Greeb Type IIb + Ib

Colorless Type IIa

145
Q

HPHT treatment

A

This is used on diamonds to alter the color centres

146
Q

Hydrothermal Synthesis

A

This places seed crystals (plates) in an autoclave with reactants and water. This creates a supersaturated solution that is cooled to produce synthetic corundum, emerald, beryl, and quartz

147
Q

Hydrothermal Systems

A

The heating of meteoric, sea, or magamatic fluids to transfer and deposit elements through subsurface “plumbing”

148
Q

Identifying a boule

A

They will have radiating circles from the spinning and progressive stepwise changes in reactant addition.

149
Q

Identifying composites

A

They will often have bubbles at the junction, feathers or other inclusions with abrupt ends at the interface. Generally look at the side to ID layers, different wear along the facets, sharp changes in luster or color, and bubbles in adhesives.

150
Q

Identifying diamonds vs. simulents

A

Most commonly this includes moissanite and cubic zirconia. Both are doubly refractive so look at the setting and see if it doubles. Alternatively, you can place the stone over a black line and if it is not a straight line it is CZ or moissanite.

Look for a sloppy cut

Look for unpolished corners. Only diamonds will have tiny parts that are left natural to maximize the carat weight.

151
Q

Identifying HPHT synthetic diamonds

A

Occasional “breadcrumbs” of metal flux

hour glass colour zoning

stronger reaction to SWUV than to LWUV

Attracted to a strong REE magnet

152
Q

Identifying hydrothermal synthesis

A

They oftentimes have small chevron or zig-zag patterns in their lattice although they are difficult to distinguish.

153
Q

Identifying Moissanite

A

It was originally only a material found in meteorites but is doubly refreactive and if set in jewelry you can look through the base to see if it doubles the image. Diamond is isometric so this will not occur.

154
Q

idiochromatic gems

A

These are gems that have transition metals integrated into their lattice to be ‘self colored’

155
Q

Imitation and Simulent Materials

A

These are natural or artificial materials that are used to imitate the effect, colour and appearence of other natural gem materials without having equivalent chemical and physical properties

156
Q

Importance of Gem Sedimentary Deposits

A

Primarily alluvial deposits of garnet, diamond, olivine, and other resilient gems.

157
Q

Impregnation and Filling

A

This is treating a stone with wax, oil, and other substances to either improve appearance, lustre, transperency, or durability. It is common in stones that may otherwise be porous or have many fractures like turquoise, jadeite, and lapis lazuli. This substance may also be colored making it a dyeing and consolidating process.

158
Q

Incipient Fracture

A

This is a directional fracture within a stone.

159
Q

Inicpiatte fracture

A

This refers to internal cracks/fractures that can or cannot reach the surface.

160
Q

Interference Colors

A

This is the result of anisotropic minerals e and o rays constructively interfering when exiting the crystal. The two add like vectors and this changes the speed and %transmission of the resultant light. This is proportional to specific mineral properties, thickness, and the light source.

161
Q

Internal features (4)

A

Inclusions, color zoning, feathers, and cleavage lines

162
Q

Internal reflections examples

A

Platelets of hematite cause sunstone’s shimmer. Copper within glass creates “goldstone”

Green mica spangles cause aventurine quartz.

163
Q

Iridescence Cause

A

This is caused by thin layers of heterogeneous solid or liquids within a material. This commonly includes exsolved feldspar (labradorite), layers of agate (fire agate), aragonite in pearl.

The different layers reflect light differently and creates the shimmering effects we see due to wave constructive/destructive interference. This is what creates the iridescence.

164
Q

Irridation types (3)

A
  1. ) high-energy neutron rays from a nuclear reactor
  2. ) streams of electrons produced by an accelerator
  3. ) gamma rays produced by a radioisotope, typically Co60
165
Q

Isometric Twins

A

Spinel (octohedral contact twins)

Iron cross (2 pyritohedrons rotated 45o apart)

Inerprenetration along {111} fluorite. This adds three fold symmetry.

166
Q

Isostructural

A

This is when there is a synonymous structure/lattice of a material but there are different elements interchanged within minerals. For example, the cation site in garnet. This is also called isomorphism.

167
Q

Isotope

A

One of two or more species of atoms of a chemical element with the same atomic number but differing masses and properties

168
Q

Isotropism

A

Mineral properties that are non-directional.

Isotropic minerals are extinct in XPL and light travels at the same speed through every direction through the material. It is a property that arises due to symmetry.

Glass, gases, amorphous solids, isometric minerals, and most liquids are isotropic materials.

169
Q

Ivory

A

This is a type of giant tooth. It can be simulated with sperm whale teeth, walrus tusk/teeth, narwhal, bear, elk, crocodile, hippopotamus, warthog teeth.

170
Q

Jet

A

This is a type of petrified wood or petrified coal.

171
Q

jewelry manufacture

A

This is the process of sending a cut stone to a factory to be faceted and polished

172
Q

KM laser treatment

A

This uses a laser to not drill into a stone but to heat it to cause a surface reaching fracture that is used to remove a dark inclusion with acid.

173
Q

LA-ICP-MS

A

Laser ablated-Inductively Coupled Plasma-Mass Spectroscopy

This is a very expensive tool that vaporizes a tiny portion of material to be quantitively analyzed by the proportions of oxides present. It is ideal for low atomic number elements and for trace elements.

174
Q

Lapidary

A

This is the art of cutting and polishing gem materials that are not diamond

175
Q

Laser Treatment

A

This is used on diamonds to reduce or remove dark inclusions. It involves using a laser to drill into a diamond until the inclusion is met. This is then dissolved to remove the unpleasant inclusion

176
Q

Lattice Defects (6)

A

Intrinsic Defects: Vacancies (missing an atom), edge/loop dislocations (when there is a terminated chain of atoms)

Extrinsic Defects: Interstitial impurity atoms (random heterogeneous atoms), precipitate of impurity atoms (a chunk of impurity), Substitutional impurity atom (substitution unlike the structure)

177
Q

Nodes

A

Nodes are collections of atoms within the lattice. They represent elements.

178
Q

LIBS

A

Laser induced breakdown spectroscopy unit

This is a type of ICP-MS unit that vaporizes a tiny portion of a stone to identify treated corundum.

179
Q

Lilly Pads

A

These are partially healed tension cracks around a small cavity or pore in peridot

180
Q

Luminescence

A

This is the emission of “cold” non-incandescent visible light. It is all emission of light from a substance. fluorescence is a type of luminescence.

181
Q

Lustre

A

This is a term that describes the surface reflectiveness/gemminess. This is influenced by hardness, reflective index (the best test for lustre), polish quality, and surface quality. It is a property that is proportional to durability.

182
Q

Mammoth vs elephant growth lines

A

Mammoth lines are at ~90o elephants are greater than 90o towards the outer edge of the tusk.

183
Q

Manebach Law

A

This is a form of polysynthetic twinning on the {001} of orthoclase

184
Q

Mineral Groups

A

These are groups of mineral series and end-members

185
Q

Mineral/Gem hierarchy

A

Supergroups: Include 3 or more groups of minerals

Groups: Includes several minerals

Species/End-Members: Individual mineral compositions

Variety: End-members that may have specific trace elements that alter their appearence.

186
Q

Mineraloids

A

These are naturally occurring mineral-like substances that lack crystalline structures. These include obsidian and opal.

187
Q

Minerals

A

A naturally occurring inorganic crystalline solid of fixed limits of chemical composition and physical properties composed of 2+ elements.

3+ minerals make rocks

188
Q

Modern, Round, Brilliant cut diamonds

A

This is the most common diamond cut that is seen very often.

189
Q

Monoclinic system, symmetry elements, and gem examples

A

a/=b/=c

α= γ= 90o

β>90o

This system is characterized by being an elongated parallelogram and has 2-fold rotational axis and/or 1 mirror plane.

Gem examples: Feldspar (K-spar only; moonstone), malachite, azurite, clinopyroxenes (diopside and jadeite), staurolite, sphene/titanite, and spodumene (kunzite).

190
Q

Monoclinic Twinning

A

Manebach law, carlsbad law, braveno law, swallow tail twins.

191
Q

Nacre

A

This is the hexagonal aragonite layers in a pearl. They are interlayered with an organic layer of conchiolin and create the iridescence

192
Q

Natural Materials

A

These are materials that have been formed by nature without human interference or modification outside of fashioning

193
Q

OA Figure

A

This will only show at a maximum three isogyres. When oriented in this direction they will be extinct in 360 rotations in XPL.

194
Q

Object reference mohs

A

masonry bit: 8.5

Steel nail: 6.5

Knife/glass plate: 5.5

Copper penny: 3.5

Fingernail: 2.5

195
Q

Observation and Magnification Procedure/Results

A
  1. ) Start with general inspection. Identify color, transparency, heft, crystal forms, and other noteworthy characteristics.
  2. ) Use the loupe to ID inclusions, lustre sharpness of facets, cleavage, fracture, and other noteworthy characteristics. Rest the loupe on your cheek bone and hold the stone at an equidistance from your loupe as the loupe is from your eye.
  3. ) Further inspection? Microscope.
196
Q

Types of cuts

A

Faceted: sharp defined edges

Cabochon cuts, rounded domes

Carvings: these are not defined by having a “base”

Cameo: These are a carving extruding from a base

intaglio: this is a carving intruding into a stone

197
Q

Optic axis

A

This is the axis within a crystal where double refraction does not occur.

Uniaxial crystals have one direction that double refraction does not occur. Biaxial materials have two.

198
Q

Optic Axis Figure (OA)

A

One of the optic axes is perpendicular to the stage and there is a partial isogyre.

199
Q

Optic normal figure

A

This is a flash figure and it represents when one of the privileged directions is parallel to the incident rays. This has the maximum level of interference.

200
Q

Optical Phenomena

A

This is a group of phenomena that articulate how light interacts with stones

Asterism: This is chatoyancy with more than one line that creates a star or some other shape. Chatoyancy is cat’s eye.

Play of color: This is the multi-colored stones that are common with opals

Iridescence: This is the multi-colored reflection of light due to thin films of material being present.

Internal Reflections/Inclusions: These are for internal objects and different substances within a material.

Scattering: This is light scatter due to irregular particles. It creates a sky-blue color with clouds.

Color Change: This is idea that some stones change color under different light sources.

201
Q

Optically Anisotropic

A

These are doubly refractive materials that shift between extinct and not extinct 4 times through a 360o rotation

202
Q

Organic/biogenic Gems

A

Carbon-based mineraloids, jet, pearl, amber, ivory, coral.

Pearls are the only gem explicitly unaltered.

203
Q

Orthorhombic System, symmetry, and gem examples

A

a/=b/=c

α= β= γ=90o

Gems: Olivine (peridot), topaz, chrysoberyl, cordierite (iolite), tanzanite

Symmetry Elements: three 2-fold rotational axis and/or 3 mirror planes

204
Q

Orthorhombic expected refractometer results

A

Two shadow lines move. This shows the material is doubly refractive, biaxial.

205
Q

Orthorhombic twins

A

Cyclical twins (aragonite)

Interpenetration twins (staurolite)

206
Q

Other diamond types

A

Red diamonds have phosphorous or deformations

Purple diamonds have H+

Green diamonds have been irridated

Black diamonds have carbon or are deep mantle diamonds (metals)

pink diamonds (Argyle mine) have dislocations

brown diamonds have dislocations that can be treated via HPHT

207
Q

Oxide Gems Examples

A

Chrysoberyl: BeAl2O4

Corundum: Al2O3

Quartz: SiO2

Spinel: MgO*Al2O3

208
Q

parallel growth

A

This is a term that refers to minerals growing with parallel edges/faces. This is a mineral cluster not a twin.

209
Q

Parallel Growth

A

This is not a twinning phenomena but describes with all faces of a crystal are formed in contact with the adjacent crystal cluster.

210
Q

Parting

A

This is “psuedo-cleavage” that occurs at discrete intervals but are not on the weakest planes.

211
Q

Pearl

A

This is the result of a mollusk covering something with nacre and organic layers of conchiolin

212
Q

Pearl X-ray Fluorescence and CT scans

A

ONLY Freshwater pearls fluoresce

Saltwater pearls with a thin nacre film around a freshwater nucleas may fluoresce.

Conch pearls are purple in x-ray radiation.

Pearls are oftentimes scanned/x-rayed to look at each individual nacre layer and identify if there is a bead at the center of the pearl.

213
Q

Pearl testing: easiest

A

Look in the drill hole for a nucleas and/or banding from a shell. Use LWUV, cultured have a green tint, Cortez Sea pearls are bright red, natural have a green tint, and general size/shape.

214
Q

Pegmatite Gems (6 gems)

A

Feldspars, quartz, beryl, tourmaline, topaz, and zircon

215
Q

Peizoelectricity

A

This is when pressure distorts the lattice of a crystal slightly to create a dipole that is used as an electric charge. It occurs in trigonal minerals.

216
Q

Peridot lilly-pads

A

This is a form of incipiatte fracture around inclusions.

217
Q

Phosphate gems

A

M+x

Character: Soft and effervescent

Apatite: Ca5(F,Cl)(PO4)3

Turquoise: CuAl6(PO4)4(OH)8*4H20

-note: Phosphates can easily replace one another. Turquoise after apatite within fossils and mineral deposits.

218
Q

Phosphorescence

A

This is a type of luminescence when materials radiates after being irridated by a high energy source. Phospherescence occurs after the high energy light is removed. In comparison fluorescence requires the stone is continually irridated to release the light.

219
Q

Physical characteristics to note in a gem

A

Habit, luster, color (colorless), heft, prisms, terminations, fracture, cleavage, crystal system, transparency.

220
Q

Physical Properties

A

This is any distinguishing property with a physical specimen that can used to ID the object.

221
Q

pinacoid

A

A pinacoid is a pair of planes that are either “side pinacoids” (parallel to c-axis) or basal (in the a-b plane)

222
Q

Plane polarized light

A

This is light that is polarized in two directions.

223
Q

Plane vs Space Lattice

A

Plane lattices are in 2d. Space lattices are 3d.

224
Q

Plastic simulants for organics sign

A

Plastic will have chips or is flaky in certain areas.

225
Q

Play of Color Cause

A

This is because of different radii of stacked spheres/globules of SiO2 that are creating opal. The gaps between spheres cause diffraction and the resultant colors. This is similar to what occurs in a rainbow. The larger the gaps the larger the range of colors.

226
Q

Pleochroism

A

This is a term for when a mineral that shows multiple colors dependent on the orientation/transmission of light. It is best seen down the OA where the fast and slow directions create different colors dependent on which polarity of light is able to travel through. There will no color change if the OA is perpendicular to the stage.

Isotropic minerals will not be pleochroic.

Report pleochroism through terms of intensity and using the dichroscope (weak, moderate, strong).

227
Q

Point system of weight

A

100 points=1 carat

50 points=.5 carat

228
Q

Polariscope

A

This is a light transmitting device that can be used to test the optics of rough, faceted, or carved materials.

It has two polarizers; the material goes between these two polarizers to be observed. The two polarizers are at 90o from one another creating XPL view or the two rays are said to be plane polarized.

It is not diagnostic but helps to classify and narrow down the search.

229
Q

Polariscope Reactions

A

Dark through a full rotation = optically isotropic, singly refractive, amorphous or isotropic.

Light and dark 4x in a full rotation = optically anisotropic and Doubly Refractive

Light through a full rotation = polycrystalline

Patchy light and dark through a full rotation = singly refractive with strain. This is anomalous double refraction.

230
Q

Polariscope use

A

Place the stone on the rotating stage and rotate the stage in 360 degree rotations. re-orient the stone and repeat. Report results

Singly refractive = extinct always=isotropic

doubly refractive= 4x extinct = anisotropic

fully illuminated always = polycrystalline

anomalous extinction = strain = polycrystalline or amorphous with strain

231
Q

Polarization of light

A

Unpolarized light has components in all directions. Polarized light is constrained to a plane. Reflected rays are polar parallel to the reflecting surface and refracted rays are partially polarized parallel normal to the refracted ray.

232
Q

Polycrystalline materials, examples, and polariscope reaction

A

Aggregates of randomly oriented small crystals or crystal fibers which need magnification to identify.

Examples: Jadeite, nephrite, chalcedony, turquoise

They are fully illuminated in the polariscope

233
Q

Polycrystalline growth

A

This is the aggregate of randomly oriented small/micro crystals/fibers.

Examples include jadeite, nephrite, chalcedony, or turquoise.

234
Q

Polycrystalline materials optically

A

These materials will never go extinct through a 360o rotation.

235
Q

Polymorphism

A

Chemically synonymous compositions with differing structures

236
Q

Pricing of Pearls: Origin

A

Saltwater=~10*freshwater

natural=~100*cultured

237
Q

Pyro Electricity

A

This is when crystals that are heated show electrical properties. This is why tourmaline in show cabinets attract dust. It is fundamentally caused by the heat causing charge diapoles in the crystals forming partial positive and partial negative zones.

238
Q

Quartz inclusions (5)

A

Rutile (brown=Brazil, Red=NC),

dumortierite (blue acicular needles from Brazil),

hematite,

brookite (silky grey lines),

petroleum,

asbestos replaced by quartz (tigers eye),

mica (aventurine),

moss agate (epidote)

239
Q

Raman Effect

A

This is the effect of shooting a laser at a substance and some of the photons scatter. Some photons interact with the electrons within the bonds of the material to excite electrons. Upon returning to a ground state this will create “scattering” characteristic to the material. This is used to identify the material.

240
Q

Raman peak intensity with bonding

A

Generally a more rigid structure (like diamond) produces very sharp peaks.

Amorphous materials produce broad peaks.

241
Q

Raman spectra light source

A

LAsers are used because they uniquely have enough energy to excite electrons. The return wavelength from the electrons is the same regardless of the source. The intensity of peaks does change with source wavelength though.

242
Q

Rarity (4 kinds)

A

Geographic Rarity: This is determined by how widespread the variety is among localles. Tanzanite is geographically rare

Historic rarity: Historic mines produce rare gems. Burma rubys, Kashmir sapphires

Quality related rareness: Abundant gems that are low quality vs rare gems at high quality (diamond)

Specific color or saturation: Gem-specific rarities like amethyst with a red/blue flash

243
Q

Reconstructed materials

A

This is the process of taking pieces of a material and re-bonding them together.

Amber can be reconstructed by heating many pieces to 200 C

Look for sharp boundaries and interesting feathers or bubbles.

244
Q

Reconstructed Materials

A

These are artificial materials made by bonding or fusing materials into a singular gem.

245
Q

Reflectance Meters

A

These are very unreliable reflectance measures.

246
Q

Refraction when a ray enters a stone at 90 degrees

A

No refraction occurs

247
Q

Refractive Index

A

This is defined as n=C/Cm this is the ratio of the speed of light in a vaccum to the speed of light in the material of interest.

n>1

248
Q

Refractometer

A

A “table” of very high RI material is used to place the flat, polished, side of a gem. Light is passed up at an angle through the table onto the stone. Because the gems’s RI is less than that of the table some of the material is reflected back and the boundary between the totally reflected light and the shadowy, partially reflected light is the shadow edge. It principally reflects light and then splits the emergent o and e rays to identify the birefringence of a stone, uniaxial/biaxial character, and if it is positive/negative.

It is a semi-diagnostic test.

249
Q

Refractometer Use

A
  1. ) remove the polarizing filter (if present)
  2. ) Prepare with the refractometer oil by placing a small drop on the glass table.
  3. ) slide a suitable facet gently over the drop. Generally, place the largest face/facet downwards.
  4. ) Keep the stone centered and look into the eyepiece at the shadow edge.
  5. ) Rotate the stone. IF no shadow edge moves the stone is ISOTROPIC (singly refractive). IF two shadow edges (seen as a partially illuminated area of the scale) move the stone is BIAXIAL. If one moves it is UNIAXIAL.
  6. ) Use the max-min to find the birefringence and report the highest values for RI.
250
Q

Relative Density

A

This is the ratio of the weight of a material to the weight of another material of equivalent volume.

In comparison to SG this does not have to be compared to water, although that is commonly the case.

251
Q

Reporting spectroscopy results

A

Materials can “cut-off” at one end of the spectrum.

There can be bright emission lines

Thick, thin, fine lines.

There are “three zones” of color. Blue, yellow, and red.

252
Q

Retail

A

This is the interface of the jewelry industry and the public. It is increasingly moving towards online sales.

253
Q

Rock Cycle

A

sed rocks to meta or weathering. meta to magma, erosion. ig to melt, meta, weathering.

254
Q

Rocks

A

These are things composed of 3 or more minerals.

255
Q

Rough dealers

A

These are dealers selling stones most proximal to the mines. This is also the locale where the greatest amount of synthetics are integrated into the supply chain.

256
Q

Ruby Asterism Natural vs. Synthetic

A

Natural: Rounded back (increases weight), off-center star, slightly fuzzy arms

Synthetic: flat back, centered star, the reflection seems to be “sitting” on the stone surface.

257
Q

Ruby fracture filling

A

This is done using a leaded glass that show blue to golden flashes an bubbles. The glass may be a significant proportion of the stone’s volume.

258
Q

Scattering Cause

A

This is caused by misalignments in the crystal structure due to inclusions (in moonstone it is albite and causes adulescence)

The scattered transmitted light is reddish/pink. The top/sides that are reflected are sky blue.

259
Q

Secondary Market

A

This is the resell market and includes pawn shops, auctions, and consignment (increasingly popular)

260
Q

Selective Absorption

A

This is the property of certain elements (primarily transition metals) to absorb most wavelengths of light and the reflected wavelengths are those we observe.

261
Q

Shadow edge

A

This is the boundary between to the totally reflected light and the partially reflected light used to indicate RI.

The other line (@ 1.79 or 1.81) is the refractometer fluid used to create a contact between the gem and the table.

262
Q

Silicate Types

A

Island/Nesosilicates: Characterized by individual tetrahedra of silicate

Paired/Sorosilicate: Tetrahedra are linked in pairs

Inosilicates: BOTH single-chain (pyroxenes) and double-chain (amphiboles) silicates

Ring/Cyclosilicates: Complex ring “sheets”

Sheet/phyllosilicates: Complete sheets of connected tetrahedra often forming hexagons connected to three other hexagons

Framework/network silicates: Connectivity of 4

263
Q

Silicates

A

Silicic acid with metal M+x

Very hard and durable

264
Q

silk inclusions

A

Usually a very fine rutile inclusion that may cause a hazy appearance in the stone, most often seen in corundum.

265
Q

Singly Refractive materials

A

These are optically isotropic materials. They are singly refractive.

266
Q

Skull Melting

A

This is used to principally produce cubic zirconia. It involves having a porous shell aka “skull” filled with seed crystals at the base and the reactents above. This is then heated with a coil that is slowly raised allowing the base to slowly cool and form CZ.

267
Q

Snell’s law

A

This says that ni *sin(i)= nr sin(r) where i is the angle from the incident ray to the normal and r is the angle from the refracted ray to the normal.

Note: the reflected ray is at i too.

268
Q

Snowflake inclusions

A

These are the white radiating patterns in obsidian

269
Q

Soudes

A

This is a triplet where the top is spinel, then there is a layer of emerald and the base is glass

270
Q

Space lattice angles

A

α= angle between B and C axis

β= angle between the A and C axis

γ= angle between the A and B axis

271
Q

Specific Gravity, and measuring SG

A

Specific gravity is defined by the ratio of the mass of material in air to the mass of displaced fluid (H2O @STP) of equal volume.

In practice it is wts(air)/(wts(air)-wts(water)). This is hydrostatic weighing

272
Q

Spectroscope

A

This requires white light that can be split into the whole visible spectrum. This light is sent through a crystal and the viewer is able to see only the transmitted wavelengths. The dark areas show areas where the gemstone has absorbed the light.

The emission spectra is characteristic of particular minerals/materials although the test is not diagnostic it can help narrow coloring elements.

273
Q

Spectroscope Use

A

Option 1: fix the stone to a source of white light using putty. Look through the spectroscope to see the spectrum. Make sure that the putty fully covers the light source and the room is dark.

Option 2: place the stone on a black or dark background. “Bounce” the light through the stone into the spectroscope.

Report emission lines, cut offs, thin, and thick lines within their given color range.

274
Q

Spectroscopy

A

This is the science of analyzing the interaction of light with a material, either visually, or mathematic analysis.

For our interests spectroscopy is related to the emission spectrum of minerals.

275
Q

Spinel diagnosis

A

Spinel is cubic and red. It commonly forms macles and has triangular pits on the pyramid faces.

276
Q

Stability

A

This is the ability of a stone to resist alteration due to light, heat, or chemicals.

277
Q

Stabilization

A

This is common with extremely porous materials that are impregnated with polymer resins to increase durability.

278
Q

Steps of artificial crystallization

A

There are two principle steps, nucleation and crystal growth.

Nucleation refers to the physical process of achieving the correct orientation of materials that equates to the crystal structure.

Crystal growth refers to the chemical process of the material growing based on the nucleated crystal. The rate and extent is related to the amount of reactants available and the environmental conditions which growth is initiated. It is generally crystallization from a melt or solution.

279
Q

Stone Beauty

A

This is a subjective measure of a stone that changes with place and time but is generally dependent on style of cut and shape, color, transperency, luster, optical effects.

It is ultimately determined by how the stone interacts with light.

280
Q

Sublimation Process

A

This is a process for producing synthetic moissanite (gem grade silicon carbide)

It involves sublimating graphite and Si C powder at 2300oC and sucking it into an Argon atmosphere where at the base of the vessel it is 2200oC and a seed crystal grows into a boule.

281
Q

Swallow tail twins

A

This is polysynthetic twinning common in gypsum along the {100} plane. It is parallel to the a-axis.

282
Q

SWUV safety

A

SWUV can cause burns. Do not stare into any UV light and do not expose yourself to SWUV to avoid sunburns.

283
Q

Synthetic lapis id

A

Iron pyrite

284
Q

Synthetic Materials

A

These are a sub-section of artificial materials that aim to mimic or replicate their natural counterparts. They have physical and chemical unity with their natural counterparts but if considered path dependent do not follow a natural path.

285
Q

Synthetic Spinel fluorescence reaction

A

SWUV: it is chalky blue/green

LWUV: it is inert

286
Q

Synthetic vs natural opal

A

Synthetic opals will have the colors “stacked” in a cross section of the stone. This is because the stone is made by allowing sphereoles of silicon dioxide fall.

287
Q

Synthetics production

A

This primarily occurs in large factories in either China or Russia

288
Q

Tagua Vegetable Ivory

A

This is an ivory simulant made from the tagua nut, a type of palm nut.

289
Q

Terms of a centered uniaxial optic axis figure.

A

Note: the isogyres show the principal planes that the o and e rays travel through.

290
Q

Terms to describe cleavage

A

Quality: Perfect, distinct, good, fair, poor

Difficulty: easy, hard, difficult. Describes how hard something must be hit to cleave.

291
Q

Tetragonal Crystal System w/ gem examples and symmetry

A

a=b/=c

α=β=γ=90o

This is a rectangular prism and the system has a single 4-fold rotational axis.

Gems: Zircon, idocrase, rutile, wulfenite, scapolite

292
Q

Tetragonal Twins

A

Cyclical Contact Twins like cassiterite and rutile. Oftentimes on the {011} plane.

293
Q

The belt

A

This is a HPHT method for diamond synthesis where diamond powder is set within a metallic flux (iron or nickel) and the capsule is subjected to extreme heat and pressure. They use a seed diamond at the base and the new crystal forms dependent on the seed crystallographic orientation, P, and T

294
Q

The colors produced by the transition elements

A

Ti: blue

V: green+pink (emerald)

Cr: red+green (ruby, emerald, alexandrite)

Mn: pink (rhodochrosite)

Fe: green, blue, red, yellow

Co: blue (spinel)

Ni: green (turquoise)

Cu: blue, green

295
Q

The mohs hardness scale reference minerals

A

10: daimond
9: corondum
8: topaz
7: quartz
6: orthoclase
5: apatite
4: fluorite
3: calcite
2: gypsum
1: talc

296
Q

Thermal and electrical conductance

A

This is important for diamond distinction. Generally, most stones are very poor conductors but diamond is a very high thermal conductor and moissanite is too. The two are differentiated because moissanite is electrically conductive and diamond is not.

297
Q

Three kinds of metamorphic protoliths

A

Metapelites: These are metamorphosed clay rocks

Metacarbonates: Metamorphosed carbonates

Metabasalts: Metamorphosed basalts

298
Q

Three types of hydrothermal

A

Hypothermal: These are the highest P and T hydrothermal deposits. 300-500 celsius

Mesothermal: Intermediate depths and pressures 200-300C

Epithermal: Shallowest depths and low T 50-200C

299
Q

tiger stripe inclusions

A

stripes along partially healed twinning planes in quartz

300
Q

Topaz: heating and irridation

A

Clear topaz can be irridated brown then heated blue. This can be further heated to be clear again or irridated to become brown again.

301
Q

Tortoise shell fake vs real

A

Real shell will be less sharp at the boundaries of the coloration whereas plastic will have sharp edges of coloration, non-diffusive.

302
Q

Total Internal Reflection

A

This is the angle (ic) of a ray where the refracted ray has r=90 so it travels along the interface of the substances and the ray of light is totally reflected back into the material.

The gemological refractometer uses TIR to measure birefringence and RI.

303
Q

Toughness

A

This is the ability for a stone to resist fracture or cleavage. It is more related to acute stresses and not long term wear.

304
Q

Transition elements selective absorption (8)

A

Ti: blue

V: green, pink

Cr: red, green

Mn: Pink

Fe: green, blue, red, and yellow

Co: Blue

Ni: Green

Cu: Green, Blue

305
Q

Transparency terms (3)

A

Transparent means that you can read through it.

Translucent means that you can see through it.

Opaque means that you cannot see through it.

306
Q

Trapiche Emerald

A

This is a hexagonal inclusion in emeralds due to carbon materials that causes sectored growth.

307
Q

Treatment and Detection

A

This alludes to the processes of both treating the rough/cut material and the latter processes of trying to identify the treatments.

308
Q

Triboelectric stones and meaning

A

This is when a stone is particular prone to static charge like amber.

309
Q

Triboelectricity

A
310
Q

triclinic system, symmetry elements, and gem examples

A

a/=b/=c

α/= β/= γ/= 90o

symmetry includes a one fold rotational axis

Gem examples: Feldspar (plag; sunstone and labradorite), kyanite, rhodonite, turquoise

311
Q

Triclinic twinning

A

Albite and Pericline twinning.

This is polysynthetic twinning perpendicular to the b axis.

312
Q

Trigonal crystal system, symmetry and gem examples

A

This is a subdivision of hexagonal w/ less symmetry where:

a=b/=c

α= 120o

β= γ= 90o

This is also said as having 4 axis (three in the x-y plane at 120 degrees and a z axis) and shows only three fold symmetry.

Gems: tourmaline, quartz, corundum

313
Q

Trigons

A

These are triangular pits that appear in the octohedron faces of diamonds that are from etching during exhumation. They are in the opposite direction of the point.

314
Q

Tringular steps

A

These are in the direction of the octahedron and show a preferred habit. Ex: Spinel

315
Q

Turquoise simulants and identification

A

“synthetic” turquoise: it does not have a groundmass and if placed into a groundmass as a conglomerate it is visible in a loupe

Reconstructured turquoise: Composites of dust and can be ided using IR spectroscopy to detect adhesive

Dyed howlite or magnesite: look for greyish marks.

316
Q

Twinning

A

This is when 2+ crystals grow together in a crystallographic relation that produces a symmetric shape. It has an abrupt change in the lattice continuity without changing the structural continuity.

It is caused by stress or a change in P/T during growth. Twins NEVER form on a previously existing symmetry plane but do increase the symmetry.

317
Q

type 1 diamonds

A

1a: nitrogen is aggregated into clusters. These started as 1b but aged and diffused. They are colorless or yellow
1b: These are younger, yellow/orange diamonds, with disseminated nitrogen throughout the lattice

1aA: These are yellow diamonds with Nitrogen pairs throughout the structure.

1aB: This is when there are 4 nitrogens around a square vacancy where the corner atoms are carbon.

318
Q

Type 2 diamonds:

A

These diamonds do not have nitrogen

2a: These have no nitrogen or boron, colorless
2b: These have dissemeninated boron atoms (B5+) they are blue

319
Q

Types of Fracture

A

Conchoidal: shell-like fracture with clam shell striations. Slightly concave. Ex: network silicates

Hackly: Breaking along jagged irregular surfaces. Common in aggregate masses.

Splintery: Long fibrous splinters

Smooth/even: There are no signs of roughness. Like in diamonds

320
Q

Types of Gem Materials (w/ examples)

A

Synthetic gems (lab-grown diamonds)

Biogenic (pearls)

Minerals (Emeralds, Rubies…)

Adornment Material (Rocks like Lapis Lazuli)

321
Q

Types of inclusions

A

Single monophase inclusion: a single liquid or gas or solid within a mineral

two-phase inclusions: more than one state of material

Three phase inclusion: all three phases present.

322
Q

Types of optical effects

A

Asterism: “cats eyes”

Chatoyancy

iridescence: labradorite

dispersion/”fire”: diamond

Play of color: opal

323
Q

Uniaxial Interference Figures

A

If aligned down the c-axis then the figure will be a distinguishable cross.

If the c-axis is not parallel to the light then you will see an arm of the figure.

If the c-axis is perpendicular to the OA then there will be a flash figure and there will mainly be a big melatope.

324
Q

Uniaxial pos vs neg in refractometer

A

The c-axis is parallel to the top facet in a uniaxial crystal and thus if the higher shadow edge moves up and down it is positive. If the lower RI shadow edge moves it is negative.

325
Q

Uniaxial systems and materials

A

Uniaxial materials are characterized by two extreme refractive indices (n) for each wavelength. They have one optic axis and have only a max and min RI.

The systems that end in ‘al’:

trigonal, hexagonal, tetragonal

326
Q

Unit Cell

A

The unit cell is the smallest repeatable unit of nodes needed to create a lattice

327
Q

Using UV light fixtures

A

Clean the material to remove dust, fingerprints, and other surface contaminants that can fluoresce.

Place the material on a black, non-reflective surface. Do not hold it in tweezers.

Minimize outside light, this is why UV cabinets are useful.

Be careful to not confuse blue reflectance and blue fluorescence.

328
Q

UV-VIS-NIR

A

Ultraviolet-visible-near-infrared spectrometer

This is a specialty tool primarily used for origin reports of sapphires, Paraiba tourmalines, emeralds, garnets, and to detect died materials.

329
Q

Verneuil Flame Fusion

A

This is a cheap, rapid, and old method for making simple oxide gems like corundum, spinel, rutile, and strontium titanate.

It is basically a long tube with a dust feed at the top followed by a furnace in the middle and an air source at the base. This enables a hot kiln in the center where the dust is fed to create a boule.

330
Q

What 4 classifications are determined through the polariscope?

A

Singly refractive

Doubly refractive

polycrystalline

strained

331
Q

What color is in the upper right of optically positive minerals?

A

Blue is in the upper right.

Yellow is in the upper right of optically negative minerals.

332
Q

What direction does light turn when entering a denser medium?

A

Light turns toward the normal, closer to vertical.

333
Q

What does inclusion interference look like?

A

This can appear like patches or changes in extinction dependent on the material.

334
Q

What extinction is exhibited in twinning?

A

This is often shown through one part of the crystal becoming extinct at different times than the other parts.

335
Q

What gem has the highest reflectivity?

A

Diamond. It reflects all of the light back out to the viewer.

Metallic surfaces are better at reflection but they are not gems.

336
Q

What hexagonal mineral will have hexagonal pits on the top and rectangular prisms on the edges?

A

Beryl

337
Q

What is a bullseye?

A

This is a uniaxial figure with a “hole” in the center that is diagnostic of quartz.

338
Q

What is a carat/?

A

It is 1/5th of a gram or the weight of one carob seed.

339
Q

What is the general relationship between weight and price?

A

Price=wtk where k>1. This is idealized where in reality it is piece-wise where big notable quanta of weights change the price (eg .9 vs 1 ct)

340
Q

What is white light?

A

It is the combination of all the colors of the visible specturm.

341
Q

When/where do interference figures appear and what is their use?

A

Interference figues are only seen down the C-axis in doubly refractive materials. It will help reveal whether the stone is uniaxial or biaxial (+-)

342
Q

Why is specific gravity or density important?

A

Stones are sold by weight. Therefore a stone with similar volume but different density will have a very different price.

343
Q

X-ray radioagraphy

A

This literally x-rays the rock for internal structure. It is used to identify pearls because they have concentric aragonite layers. It is very fast too, ~15-20 minutes

344
Q

Yield

A

This is the comparison of the weight of stone retained after cutting vs. the rough weight. Generally, stones are fashioned to increase yield.

It can either be said as a percent or as an absolute weight.

345
Q

Zircon common forms

A

Zircon is tetragonal but often the c axis is not too long making it seem bipyramidal.

346
Q

Zone Melting

A

This used a conglomerate or sintered rod that is then heated by passing a heating coil along the rod and feeding reactent as it moves to enlarge the rod.

347
Q

Girdle

A

This is the fine band around the widest part of the modern round brilliant cut that is used to secure the stone in jewelry

348
Q

Pavillion

A

This is the term referring to the part of the facet that is below the girdle in includes the lower girdle facet, pavilion main facet, and the cutlet.

349
Q

Crown

A

This is the area above the girdle. It includes the table, upper girdle facet, and crown main facet.

350
Q

Other facet styles

A

Step cuts: Emerald (tapered rectangle) and Baguette cut (trapezoid)

Rose cut: This is the oldest facet and it is a disco ball on the top and a flat bottom

Mixed Cuts: These include more than one type of faceting style

Fantasy cuts: These are particularly popular right now and create unique internal inclusions

351
Q

Baroque

A

These are irregular polished and tumbled stones. It also applies to irregular pearls.

352
Q

Cabachon styles

A

There is medium, flat, double (rounded top and bottom), and hollow (used with garnet to increase transperency) cabochons

353
Q

Cabochon cut reasons

A

Cabochon cuts may be preferred if the stone is translucent or opaque, reveal optical effects, or to maximize the durability of softer stones.

354
Q

Beads

A

These are polished or faceted materials with a hole in the middle

355
Q

Inlays

A

This is popular in native american jewelry and includes flat pieces of stone arranged to create unique patterns.

356
Q
A

GEOS 260 (1 decks)

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