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Rocks, Minerals, and Gems > Diamond > Flashcards

Diamond Flashcards

1
Q

Etymology of diamond

A

Greek adamao, I tame/I subdue, 1st c. BC
- also root for adamantine (lustre like a diamond)
- used to denote great hardness

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2
Q

Earliest use of diamond

A
  • first mining occured in India (alluvial deposits)
  • Sanskrit vajra, 4th c. BC
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3
Q

Significance of kimberlite

A

Diamond-bearing kimberlite discovered at Kimberley, South Africa in 1867 resulted in upper and middle classes having access to diamonds

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4
Q

Main diamond producing countries

A

India (alluvial deposits, prior to 20th c)
Brazil (18th c)
South Africa (1867)
Soviet Union (1950s)
Australia (1980s)
Canada (1990s)

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5
Q

Basic qualities of diamond

A
  • pure carbon
  • dense crystalline structure (3.51 g/cm3)
  • cubic symmetry
  • perfect octahedral cleavage
  • Mohs value of 10
  • high durability
  • high refractive index (2.42)
  • great dispersion
  • colourless (can show colour due to structural defects, elemental substitution, and lab procedures)
  • can fluoresce under UV
  • hydrophobic; sticks slightly to grease
  • very high thermal conductivity
  • low electrical conductance
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6
Q

4Cs of diamonds

A

Colour
Cut
Clarity
Carat

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7
Q

Thermal conductivity of diamond

A

Very high due to covalent bonding of the carbon atoms
- 3x higher than gold and silver

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8
Q

Electrical conductivity of diamond

A

Low
- unusual when paired with high thermal conductance

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9
Q

Crystal structure of diamond

A

Cubic/isometric crystal system
- each of the crystallographic axes is the same length at 90 degrees to one another (unit cell building blocks are simple cubes)
- very strong covalently bonded carbon atoms & highly symmetrical 3D network
–> hard, durable, dense

Tetrahedron - each carbon atom is bonded to four other carbons in perfec triangular pyramid shape

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10
Q

What is diamond’s weakness?

A

Cleavage planes intersect to form octahedron

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11
Q

Facets

A

flat parts on a polished stone

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12
Q

Polymorph

A

A material of the same composition but with a different crystal structure

Eg.
graphite and diamond both have composition “C”
- in diamond, covalent bonds and cubic crystal system
- in graphite, 2D bonds are strong, but weak Van der Waals bonds between planes (sheets)

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13
Q

How diamonds are grouped

A

Gemologists and jewellers: 4Cs
Scientists: crystal chemistry variations

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14
Q

Crystal Chemistry Classification

A

Nitrogen substitution
- Type I –> N > 10 ppm
- Type II –> N < 10 ppm (N-free)

Dispersion of the nitrogen
- Type Ia –> N atoms occur in aggregates within the diamond (~98% of diamonds)
- Type Ib –> N is dispersed iwthin diamond structure

Clustering of the nitrogen
- Type IaA –> N atoms are paired
- Type IaB –> N atoms occur in quads (clusters of 4, often with vacancy at centre)

Boron content
- Type IIa –> B-free (2nd most common type @ <2%)
- Type IIb –> minute (<10 ppm) amounts of B (very rare)

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15
Q

Colouring of each type (crystal chemistry classification)

A

Yellow hue (absorption of blue light)
- Type Ia (appreciable N, clustered)

White (lack of impurities; no absorption of light across visible spectrum)
- Type IIa (no appreciable N or B substitutions)

Blue to grey hue (most light except blue is absorbed)
- Type IIb (minute B, no appreciable N)

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16
Q

Cause of colour - colourless

A

No impurities

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17
Q

Cause of colour - Blue to grey

A

Boron impurities

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18
Q

Cause of colour - yellow to orange, subdued to intense, or almost colourless

A

Nitrogen impurities

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19
Q

Cause of colour - pink, purple, red, cognac

A

Deformation of crystal structure (hypothesized)

20
Q

Cause of colour - green

A

Natural irradiation (exposure to radiation)

21
Q

Cause of colour - black

A

Abundant graphite and other opaque inclusions

22
Q

Chameleon diamond

A

Thermochromic - change colour upon gentle heating

23
Q

Possible habits/shapes of diamond

A

Most common
- Octahedron

Common
- Cube
- Octahedron modified by cube faces, or cube modified by octahedron faces

Uncommon
- Dodecahedral
- Twinned
- Macle (flat tabular form)
- Polycrystalline aggregate

Corrosive modification during transport can round edges of primary crystal growths; multiple growth and corrosion events can lead to highly complex shapes

24
Q

Common imitations for diamond

A

Moissanite (higher dispersion, greater refractive indices, not isometric)

Cubic zirconia (lower thermal conductivity)

Glass (lower thermal conductivity)

Strontium titanite (lower thermal conductivity)

Yttrium-aluminum-garnet (lower thermal conductivity)

25
Q

Common treatments for diamond - colour altering

A
  • HPHT annealing (high pressure, high temperature)
  • LPHT annealing (low p/high t)
  • Irradiation
26
Q

HPHT annealing

A
  • most common colour treatment for diamonds; most often removal of brown body colour/removing or enhancing existing yellow
  • increase temperature while maintaining very high pressure
  • prevent graphitization
  • crystal structure altered (combination states of nitrogen impurities –> change between Type Ia and Ib)
  • can heal lattice vacancies
27
Q

Common treatments for diamond - clarity

A
  • Glass filling (lead-bismuthate glass fills in fractures that reach surface of stone)
  • Laser-drilling (high powered laser can reach impurities otherwise sealed from surface; followed by acid boiling and glass filling)
  • Acid boiling (acid either bleaches or dissolves inclusion out)
28
Q

Synthetic diamond production methods

A
  • Chemical Vapor Deposition (CVD)
  • High Pressure High Temperature growth (HPHT)
29
Q

Where can diamonds be found?

A

Primary deposits
- volcanic rocks on the surface (kimberlite, lamproite)
- un-erupted magma that feed volcanoes

Secondary deposits
- include diamonds that have been moved from primary source and concentrated in a new location (rivers, nearshore currents)

30
Q

What conditions allow for diamond growth (the Diamond Window)?

A

Keel of Archean craton
- depth > 140 km (high pressure >50,000 atmospheres)
- “cool region” between 950-1400°C (typical temperature at 140 km depth is ~1500°C)

31
Q

Kimberlite magmas

A
  • generated at base of craton (200-300km depth), ascend very quickly (picking up diamonds in their path; high speed prevents transformation into graphite and chemical alteration), and erupt in special volcanoes, depositing diamonds on surface
32
Q

Kimberlite volcanoes

A
  • diatreme –> vertical, carrot-shaped body, typically up to 1km across at surface
  • very explosive –> magma interacts with groundwater
  • magma travels rapidly; as depth and pressure decreases, magma propogates faster and faster
33
Q

Indicator minerals

A

Other minerals occurring in diamond-bearing kimberlites
–> presence on surface can indicate nearby kimberlite rocks
- green olivine
- purple pyrope garnet
- chromium-bearing diopside
- chromium-bearing spinel
- ilmenite (iron titanium oxide)

34
Q

Kimberlite

A
  • the major source of diamonds
  • a form of peridotite (intrusive igneous rock; coarse grained, dark-coloured, dense; min. 40% olivine)
  • mica-rich
  • occurs in pipes (intrusive igneous bodies with vertical sides; <1km diameter)
  • found in uplifted centres of continental platforms; formed during Late Cretaceous period (100-65mil years ago)
35
Q

Lamproite

A
  • similar to kimberlite; hosts diamond (less commonly)
  • unlike kimberlites, can exist in areas outside of Archean cratons
36
Q

Why is diamond rare?

A
  • formational environment is well below surface; only special geological conditions allow transport upwards
  • not as rare as De Beers wants you to think
    –> 140 million carats mined annually
37
Q

Archaen craton

A

Archaen –> older than 2.5 billion years (to 4 billion); the earlier eon of the two formal divisions of Precambrian time (about 4.6 billion to 541 million years ago) and the period when life first formed on Earth.

Craton –> a large, coherent domain of Earth’s continental crust that has attained and maintained long-term stability. Reworked crust only becomes a craton once the cumulative tectonic, magmatic, and metamorphic reprocessing has self-organized the crust and underlying lithosphere into a stable density, compositional, and thermal profile

38
Q

4 Cs

A

System introduced by GIA in 1940’s
Cut
Clarity
Colour
Carat

Bonus: 5th C
Country of origin (proposed)

39
Q

Cut

A

The external anatomy of a gemstone; the quality of the facets that define the gemstone’s proportions
ie., the way facets are cut (not the shape)

Grading assessment
- quality of facets and their polish
- physical proportions of the stone
- girdle diameter, angles for crown and pavilion
- excellent/ideal (good symmetry of facets; good length to width ratios)- very good - good - fair - poor

40
Q

Anatomy of a round brilliant-cut diamond

A
41
Q

Facet names of a round brilliant-cut diamond

A
42
Q

Clarity

A

The internal and external imperfections of a stone
Often present in rough form; diamond cutters will often sacrifice carat weight to improve clarity

Six-tiered grading system
I (included) to FL (flawless)

Flaws:
- solid mineral inclusions (most common)
- fluid-filled inclusions
- clouds
- feathers
- scratches
- abrasions
- burns

43
Q

GIA clarity grading subdivisions

A

Stones are examined under 10X magnification

Flawless (FL): no blemishes or inclusions

Internally flawless (IF): no inclusions, insignificant blemishes

Very very slightly included (VVS1 > VVS2): contains minor inclusions, very difficult to locate

Very slightly included (VS1 > VS2): contains minor inclusions (difficult –> easy to see)

Slightly included (SI1 > SI2): contains noticible inclusions

Included (I1 > I2 > I3): contains obvious inclusions that may affect potential durability, transparency, and/or brilliance

44
Q

Colour

A
  • almost all diamonds have yellow undertone

Colour scale:
- D (colourless) to Z (deep yellow, considered undesirable)
- beyond Z: fancy or fancy intense (saturated enough to be unusual, more desirable)

45
Q

Carat

A

Total weight of the stone
- one carat is equal to 0.2 grams (or 100 points)
- 5 carats equal 1 gram (or 500 points)

46
Q

Shapes

A
  • designed to maximize brilliance and fire, or intensify colours
47
Q

Kimberly Process (Certification Scheme)

A

Mandate: “to address the development, implementation, and oversight of a tracking system for the export and import of rough diamonds to prevent the exploitation of diamonds for illicit purposes such as war and inhumane acts”

81 countries are involved
- 99.8% of global diamond production

Rocks, Minerals, and Gems (18 decks)

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