Terms Flashcards
The term used to describe a gem that is colored by trace elements in its crystal structure is
allochromatic. In an allochromatic gem, the pure state can be colorless, and color is only achieved when certain trace elements are present in the crystal lattice
In gems, phenomena caused by structure are the result of
interference. Interference is the interaction between two light rays with the same wavelength as they travel along the same path.
ie Moonstone, labradorite, opal
The characteristic shape of a gem crystal is called its
habit. A mineral’s characteristic shape, or habit, depends on its growing conditions.
The type of deposit that’s most likely to be found miles away from the original source rock is
An alluvial deposit is a type of secondary deposit where gems have been eroded from the source rock and transported by water far from their source.
Which is a workable alluvial deposit of gem minerals with economic potential?
placer. When an alluvial deposit shows economic potential, miners refer to it as a placer.
The kinds and relative quantities of atoms that make up a material are defined as its
chemical composition. The kinds and relative quantities of atoms that make up a material are defined as its chemical composition
A rock must
Rocks are composed of masses of one or more kinds of mineral crystals
A regular, repeating internal arrangement of atoms in a material is its
crystal structure. A regular, repeating internal arrangement of atoms in a material is its crystal structure.
A quantity of stones of similar or mixed qualities, from a single mine or from various sources, offered for sale together is called a
parcel. Quantities of stones are commonly sold in parcels
Which trade term describes a mixture of gem qualities that represents unsorted production from a particular mine?
mine run
A natural, inorganic substance with a characteristic chemical composition and usually characteristic crystal structure is a
Minerals are natural, inorganic substances with a characteristic chemical composition and usually a characteristic crystal structure
A substance that consists of atoms of only one kind is a
A chemical element is a substance that consists of only one kind of atom.
A broad gem category based on chemical composition and crystal structure is a
species
Rocks altered by heat and pressure are
metamorphic. The heat and pressure of metamorphic processes transform rocks into new rocks
A deposit where gems are found in the rocks where they formed is called
primary
Which is a deposit where gems eroded from the source rock and remained in place nearby?
Eluvial deposits are a type of secondary deposit in which the gems are eroded from the source rock but not transported as they are in alluvial deposits
Atoms in a gem that are not part of its essential chemical composition are
Trace elements are trapped in a growing crystal, but they’re not necessary for the crystal’s growth, and they’re not part of its essential chemical composition
A unit cell defines a mineral’s
basic identity. The unit cell is the smallest group of atoms with the same chemical composition and crystal structure as the mineral. The unit cell is the mineral’s “signature”—its basic identity
Which type of twinning looks as if two crystal halves are mirror images?
contact. The two crystal halves of contact twins look like mirror images of each other. This is common in spinel
Which aggregate’s crystals are visible only under very high magnification?
cryptocrystalline. Detecting the small crystals that compose cryptocrystalline aggregates requires magnification that is beyond the power of standard gemological microscopes.
Which type of twinning is caused by environmental change after the gem forms?
Polysynthetic or lamellar twinning is a type of secondary twinning that occurs after the gem has formed when the rocks it formed in are altered by pressure from metamorphism.
How heavy an object is in relation to its size is called its
density. Some minerals are made of heavier elements than others, or have atoms that are closer together.
When a gem’s crystal structure splits light into two rays that each travel at a slightly different speed and direction, it’s called
double refraction. Most colored stones are doubly refractive, and their crystal structure splits light into two rays that each travel at a slightly different speed and direction
The pattern of dark vertical lines or bands shown by certain gems when viewed through a spectroscope is called
absorption spectrum. The spectroscope can show a characteristic pattern of dark lines and bands known as an absorption spectrum
The process where electrons that selectively absorb light are passed back and forth between neighboring impurity ions is known as
Charge transfer occurs when electrons that selectively absorb light are passed back and forth between neighboring impurity ions
A gem colored by an element that is part of its basic chemistry is called
idiochromatic.
Adularescence is caused by
Light scattered by the internal structure of moonstone causes its adularescence
Which phenomenon is a broad color flash?
Labradorescence
Which process dissolves nutrients in chemicals to form synthetic crystals?
flux growth.Chemicals dissolve the nutrients needed to form synthetic crystals by the flux growth process
Synthetic opal is grown using microscopic silica spheres that are produced by
precipitation. The chemical process used to produce microscopic silica spheres for growing synthetic opal is called precipitation.
Which synthetic process developed rapidly due to laser research in the 1960s?
The pulling process was developed to meet the need for inclusion-free synthetic ruby in laser equipment.
Low cost and high volume characterize which process?
The flame-fusion process produces a large volume of synthetic gems at low cost
Which process uses a heating unit that passes over a rotating solid rod of chemicals until it forms a synthetic crystal?
floating zone. a chemical rod rotates as a heating unit passes over it. This causes the material in the rod to crystallize in “zones” that eventually transform the rod into a single crystal
Which synthetic process uses an autoclave?
Hydrothermal growth. steel autoclave container
The crucibles that work best for flux growth are made of
platinum. The chemicals used in the flux process are very corrosive. Platinum is highly resistant to corrosion and works best for this process
Quartz or topaz with a thin layer of gold deposited on the surface is known as
aqua aura
What is a Single Phase inclusion
Liquid Inclusion
A smooth, flat break in a gemstone parallel to planes of atomic weakness, caused by weak or fewer bonds between atoms, or both
Cleavage
A flat break in a gemstone caused by concentrated included minerals parallel to a twinning plane.
Parting
Any break in a gem other than cleavage or parting, not feather
Fracture
3 Types of Igneous Formation
- Volcanic
- Pegmatites
- Superheated Water/ Hydrothermal
3 types of Metamorphic Formation
- Regional Metamorphism
- Contact Metamorphism
- Metasomatic
2 types of Sedimatary Formation
- Gems formed by Water Near Earths Surface
- Geode Formation
Clarity enhancement is…
the practice of filling gem fractures with a variety of substances to increase transparency and improve color and overall appearance.
“Kashmir” aka Cornflower describes sapphires that have a _______ blue to _______ blue hue, with moderately strong to vivid saturation and medium-dark tone. Minute
inclusions can give the gems a velvety appearance and desirable softness,
and also intensify their color.
violetish, pure
“Burmese” describes sapphires with a slightly________ blue to blue hue. Their
blue can be more intense and saturated than Kashmir sapphires. ________ under
incandescent light
violetish, inky
“Ceylon” and “Sri Lankan” refer to sapphires that generally have a
violetish blue to blue hue, with slightly_______ to strong saturation and
light to medium-light tone. The light tone means more light returns to the
viewer’s eyes, so these sapphires tend to be more _______
grayish, brilliant
________________ is the most common sapphire synthesis method
Flame fusion
Variations in conditions and coloring agents that occur during crystal growth can result in color _____________
zoning
In practice, what GIA Colored Stone Grading TONE levels apply to transparent colored stones?
TONE 2-8
The first impression of an object’s basic color is its
hue
When a singly refractive stone shows a second color face-up, this is called
light reflected within the stone interact with light transmitted through it
Extinction results from ________ _________, while shallow ones typically cause _________
deep pavilion, windows
Removing heavily included sections from gemstone rough by carefully tapping it with a small hammer is known as
cobbing
When viewed face-up, a stone with more than 75 percent brilliance is considered to have
excellent proportions
60 and 75 percent very good.
40 and 60 percent pretty good
25 and 40 percent fair
25 less poor
Which type of rough is usually faceted?
Transparent
A carved design that projects slightly from a flat or curved surface is called a(n)
cameo
Which cutting stage has the greatest impact on the value of the finished gem?
preforming
Important factors in evaluating a faceted gem’s proportions are its _______ and_________ depths, the________ of its profile, and its face-up outline
crown, pavilion, symmetry
____________ gems are the most likely to undergo cobbing
Lower-cost/ commercial quality
Rough that’s ground to the approximate shape of the finished stone is called
preform
An angular, hollow space that resembles a mineral inclusion is called a
Negative crystals are angular hollow spaces that resemble mineral inclusions
Fingerprints are
partially healed fracture planes.
The five factors that determine an inclusion’s impact on a gem’s value are
nature, size, number, position, and relief
Growth zoning in a colored stone is evidence of
crystal growth
In which of the following colored stone clarity grades do the definitions vary for each clarity type?
Moderately included
The clarity differences in definition between the________ included and___________ included grades of each clarity type are especially important. The distinctions between them
might seem subtle, but they can make a considerable difference in value
slightly, moderately
What category of colored stone is often sold per piece?
small, calibrated amethyst, peridot, garnet, citrine, and fire opal by the piece. Per-piece pricing for small, inexpensive gems helps commercial jewelry manufacturers track their expenses.
A gem’s price divided by its carat weight is called
per-carat price
Individual stone prices are referred to as
Unit price
How many points are in a metric carat?
100
Sieves are most useful for sorting round gems with diameters _________ and below
3mm
A metric carat equals _________ grams
.20
Most colored stones are sold by __________
weight
__________typically have the highest per-carat value of all fancy sapphires
Padparadschas
The finest yellow sapphire is yellow to_______ yellow, with medium tone and vivid
saturation.
orangy
Orange sapphires range from yellowish orange to reddish orange in light to dark tones and all degrees of saturation. The finest orange sapphires are strongly________-orange with medium tone and vivid saturation
red
Green sapphire results from a mixture of two different color-causing mechanisms: yellow, caused by_______, and blue, caused by an iron and titanium intervalence charge transfer.
iron
The least expensive and perhaps most commonly seen star sapphires are
black stars from _______ and __________
Thailand and Australia
Generally, gem weight is stated to the nearest
hundredth of a carat
The trade term “____________” is often used to describe emeralds that are slightly darker and more bluish than “Colombian” emeralds
Zambian
The organ that lines the mollusk’s shell, encloses its soft body, and contains the cells that form pearl sacs and secrete nacre
mantle
The natural substance produced by pearl-bearing mollusks to make pearls.
Nacre
A crystallized form of calcium carbonate found in nacre
aragonite
The organic “glue” in nacre that holds aragonite platelets together
Conchiolin
The nacreous layer inside a pearl-bearing mollusk’s shell
Mother-of-pearl
Optical phenomenon created in some non-nacreous pearls when intersecting groups of crystals interact with light
flame structure
A bead used as the core of a cultured pearl, usually made from a freshwater mussel shell
bead nucleus
A bead used as the core of a cultured pearl, usually made from a freshwater mussel shell
Mantle-tissue piece
Tissue that encloses an implanted bead nucleus and mantle tissue piece, or the piece alone, and secretes nacre to form a cultured pearl
Pearl sac
Common name for the Pinctada fucata oyster and the natural or cultured pearls it produces
Akoya
Tahitian Peacock is the trade term for a dark green-gray to blue-gray bodycolor with______ to ________ overtones. It’s often the most highly valued color
pink to purple
A three-step freshwater cultivation process involving a series of distinct growth periods
Coin-bead/spherical-bead (CBSB) production
Product that results when a pearl-bearing mollusk is returned to the water after the first harvest
Second-generation cultured pearl
A number of similar cultured pearl strands bundled together
Hank
A company that prepares cultured pearls for the market
Processor
assembled cultured blister pearl.
Composed of a nacre dome, filler, and a mother-of-pearl backing
Mabé
Golden pearl—Strong_______ yellow to________ yellow South Sea cultured pearls
greenish, orangy
Pistachio pearl—Tahitian cultured pearls with a_________ green to_________ yellow bodycolor
yellowish, greenish
Luster in pearls is caused by light traveling through translucent layers of nacre and reflecting back to the eye. The nacre’s thickness, its degree of translucence, and the arrangement of the overlapping nacre layers all
contribute to luster
Lustre
Trade name for the finest quality, semitransparent jadeite with even, vivid green coloration
Imperial
An uneven distribution of color against a contrasting background
Mottling
Gemstone jewelry carved entirely from a single piece of rough
Hololith
Spots of color near the surface of a jadeite boulder, where the skin is thin enough to allow color to show through
Show points
A trade name for top-quality white nephrite
Mutton-fat jade
Rough nephrite extracted directly from primary deposits
Mountain jade
Opal that lacks play-of color
Potch opal, non-precious
In this model, seasonal rainwater soaks the dry ground in opal’s arid source areas. The water dissolves the silica as it trickles downward and deposits it in voids and cracks in the rocks. Much of the water evaporates during the dry season, leaving a solid hydrous silica deposit behind. This hydrous silica deposit is opal.
The Weathering Theory
A gem material’s host rock, which sometimes becomes part of the finished gem ie. boulder opal
Matrix
An opal’s bodycolor, independent of its play of- color
Background color
A manmade glass opal imitation with scattered, tinsel like colored flakes that imitate play-of-color
Slocum Stone
A cryptocrystalline quartz aggregate
Chalcedony
Chalcedony with curved or angular bands or layers that differ in color and transparency.
Agate
Transparent quartz, usually rock crystal, that contains eye-visible inclusions, often named
according to the type of inclusions it contains ie. Rutilated quartz, toumralinated quartz
Sagenitic quartz
A type of sagenitic quartz containing needle-like rutile inclusions
Rutilated quartz
A type of sagenitic quartz containing needle-like or rod-like tourmaline inclusions
Tourmalinated quartz
Unlike most chatoyant gems, neither _______-eye nor__________-eye requires a curved surface to display chatoyancy
tiger’s, hawk’s
A property of some crystals that causes them to generate an electrical charge when subjected to mechanical stress
Piezoelectricity
A crystal growth habit in chalcedon with a bumpy appearance similar to a bunch of grapes
Botryoidal
A procedure that includes cleaning, buffing, and sometimes bleaching, done to make cultured pearls presentable and appealing, is called
Processing
The matching level that describes a group of pearls with minor variations in uniformity is
Good
* Excellent—Pearls are uniform in appearance and drilled on center
* Very Good—Very minor variations in uniformity
* Good—Minor variations in uniformity
* Fair—Noticeable variations in uniformity
* Poor—Very noticeable variations in uniformity
Play-of-color that’s seen only when light travels through an opal to the eye is called
contra luz
Which treatment involves immersing opal in concentrated sulfuric acid?
sugar
Who created the first marketable synthetic opal?
Pierre GILSON of Switzerland, synth emerald
“Marabá” amethyst is often
uniform in color
Tanavyte is a trade name for
purple synthetic YAG
Nacre is composed primarily of
aragonite and conchiolin
A trade term for hydrogrossular garnet is
Transvaal jade, african jade
When the outline of an earlier growth phase is visible within a quartz crystal, this is called
the phantom effect
All quartz varieties can be divided into three broad categories based on crystal size:_________ crystal, microcrystalline aggregates, and cryptocrystalline aggregates
single
Which stone is known as the cross stone?
Chiastolite andalusite
A widely used trade term for gem-quality topaz of medium reddish orange to orange-red color
Imperial topaz
Chromium causes natural pink, red, and violet-to-purple colors in topaz.
Color centers cause yellow, brown, and blue.
If both chromium and color centers are present, the topaz will be orange
Because of its___________, topaz requires special care in cutting, polishing, mounting, and wear
basal cleavage, parallel to base
A trade term for orange-to-yellow and brown topaz
Precious topaz/ sherry
Topaz heat treated to pink or irradiated and heated for blue are
stable
The finest aquamarines are a moderately strong, ___________-__________ blue to slightly greenish blue
medium-dark
Gems that show color zoning with two or more colors
Parti-colored
A tourmaline, usually elbaite, with color zoning made up of a pink central zone
surrounded by a green overgrowth
Watermelon tourmaline
Trade term for a vibrant green tourmaline that’s colored by traces of vanadium, chromium, or both
Chrome tourmaline
Trade name for pink to red elbaite tourmaline
Rubellite
Trade term for rare, expensive, vibrant green to blue or violet elbaite tourmaline, originally found only in Brazil’s Paraíba state
Paraíba tourmaline
Trade term for blue tourmaline.
indicolite
A mineral that’s been broken down from a crystalline to a partly amorphous state by
emanations from radioactive impurities. In LOW zircon, green
Metamict
A cabochon with a curved, undercut bottom, designed to lighten the tone of the gem material
Hollowback
Substitution of one chemical element for another in the crystal structure of a mineral
Isomorphous replacement
A trade term for polymer-impregnated turquoise
Stabilized turquoise
A turquoise imitation made of a mixture of powdered minerals, dyed and bonded with plastic or epoxy resin
Reconstructed turquoise
Trade term for a highly prized, vivid blue adularescence displayed by the finest moonstone
Blue sheen
Tiny tension cracks in moonstone that interfere with adularescence and reduce value.
Centipedes
An imitation of aventurine feldspar made of glass that contains small copper crystals
Goldstone
Horsetail inclusions are found in
Demantoid
The trade term malaya is used for a pinkish orange garnet that’s a mixture of
pyrope, spessartine, and almandine
A treatment that makes turquoise less porous without the use of polymers and improves its ability to take a good polish is
Zachary method
polymer-impregnated turquoise is called
Stabilized turquoise
Rainbow moonstone is a trade term for a type of
It’s a variety of labradorite, a plagioclase-series feldspar
Immature amber is known as
Copal
a Maori name for abalone shell
Paua
___________A laboratory creation with essentially the same chemical composition, crystal structure, and properties as its natural counterpart
___________Any material that looks like a natural gem and is used in its place.
Synthetic gem vs Imitation gem
A synthetic-crystal growth method in which the chemical mixture is melted, then recrystallized
Melt process.
Ie Flame fusion, pulling, boule, floating zone
A growth method in which the synthetic crystal grows from a dissolved chemical mixture,
sometimes at high temperature and pressure
Solution process
ie. flux growth, hydrothermal
A process in which powdered chemicals are dropped through a high-temperature flame
onto a rotating pedestal to produce a synthetic crystal.
Flame fusion. Auguste Vernuiel
$5 or less
A process in which the synthetic crystal grows from a seed that is dipped into a chemical melt, then pulled away as it gathers material
Pulling, sapphire synthesis
$5 x 10
laser research
A melt process where a heating unit passes over a rotating solid rod of chemicals until it forms a synthetic crystal
Floating zone. 1953,
responding to a need for high-quality silicon semiconductors
A synthetic-crystal growth method that uses cooling pipes around an interior of melted
chemical ingredients
Skull melt. high-temperature technique that produces CZ
A process in which nutrients dissolve in heated chemicals, then cool to form synthetic crystals
Flux growth: crucible, seed crystal
emerald, rubies, sapphires, alexandrites, and spinels
$100/ct
A process in which nutrients dissolve in a water solution at high temperature and pressure, then cool to form synthetic crystals.
Hydrothermal growth. steel autoclave, seed cystal
quartz
$100/ct
A synthetic crystal growth method that starts without a seed crystal
Spontaneous nucleation
_________________Two or more separate pieces of material joined to form a unit
_________________A single assembled stone made from three separate pieces of material fused or cemented together, or from two pieces and a colored cement layer
Assembled stone
Triplet
Direction of single refraction in a doubly refractive gem
Optic axis, no double refraction direction
Continued emission of visible light
after UV or X-ray stimulation stops
Phosphorescence
A process where two transition elements with different valences exchange electrons to selectively absorb light
Intervalence charge transfer
A small defect in the crystal structure of a material that can absorb light and give rise to a color
Color center
A special kind of interference phenomenon that produces patches of pure spectral colors ie opal, labradorite
Diffraction
Localized changes caused by an igneous intrusion that takes place where the magma meets the surrounding rock
Contact metamorphism
An igneous rock typically formed from cooling, once-molten granite that follows fractures in its surrounding rock
igneous rock - Rock formed by the crystallization of molten material
Pegmatite
A deposit where gems are eroded from the source rock but remain in place close to the source
Eluvial deposit
A type of metamorphism where chemical changes in the minerals and rocks result from
the introduction of material from external sources, often as hydrothermal solutions
Metasomatism
Changes in rock type and minerals over a wide area, caused by heat and pressure of large-scale geological events
Regional metamorphism
Rock produced from the eroded and weathered remains of existing rocks
Sedimentary rock
Large mass of igneous rock that crystallizes underground without reaching the surface
Intrusion
Crystallization of minerals from a gas
Pneumatolysis
___________ A family of gems from several closely related mineral species
___________A broad gem category based on chemical composition and crystal structure
___________A subcategory of species, based on color, transparency, or phenomenon
Group
Species
Variety
Impurities and defects provide additional energy levels in some gems’ band gaps. Electrons can more easily make transitions between these energy levels within the band gap by selectively absorbing visible light and producing color
Band theory
Gem color is produced when electrons of individual transition
element ions selectively absorb some wavelengths of visible
light
Transition element
structure Squat and flat, like many corundum crystals
Tabular
structure Columnar, with 3, 4, 6, 8, or 12 parallel faces. ie aquamarine and tourmaline crystals
Prism or prismatic
structure Well formed, with sharp crystal faces, like most gems from pegmatite pockets
Euhedral
structure Lacking obvious crystal faces, like many gems that have been tumbled in rivers
Anhedral
structure Horizontal (quartz, corundum) or vertical (tourmaline, topaz) growth markings on a crystal
Striations
structure Shape with equal triangular faces that meet ina point
Pyramid
structure Shape with two pyramids back-to-back. Seen in sapphires, for example
Bipyramid
