eosc lesson 9

basic definition of diamond and its basic qualities?

basic definition of diamond and its basic qualities?

pure carbon packed in a dense crystalline structure, chem formula = C

• cubic symmetry

• perfect octahedral cleavage

• 10 on Mohs hardness scale

• high durability

• high refractive index (2.42)

• great dispersion

• pure diamond = colorless

what causes the very high thermal conductivity of diamonds

strong covalent bonds between C atoms in crystal lattice

• X3 higher than gold and silver’s, & much higher than simulants’

  • except moissanite, which is similar

diamond’s low ________ ________ paired with high thermal conductance is unusual

electrical conductance

describe diamond’s crystal structure

• cubic (isometric)

• strong covalent-bonded C atoms, highly symmetrical 3D network

  • each C atom bonded to 4 others in tetrahedron

• perfect cleavage (structural weakness)

Describe the cleavage of diamond

• perfect cleavage (structural weakness)

• cleavage planes intersect, forming octahedron shape

what are cleavage planes

imaginary flat planes of weakness in a mineral’s atomic structure where it can break

describe the importance of diamond cleavage for diamond cutters

diamond cutting requires understanding of its crystallography/weaknesses to:

• expertly cut them

• grind flat parts (facets) on polished stone

describe the type Ia diamond (composition/most common color).

composition:

• contain significant amounts of CLUSTERED nitrogen in crystal structure

• N atoms occur in aggregates as pairs/quads often with vacancy at center

most common color:

• yellow hue

  • caused by N presence, which creates color centers absorbing blue light

• also colorless, pink, orange, green, violet

describe the type Ib diamond (composition/most common color).

composition:

• contains DISPERSED nitrogen in structure

  • hence, different crystal structure/optical properties than Ia

most common color:

• tends to be less yellow than Ia; range of yellow, brown, orange

describe the type IIa diamond (composition/most common color).

composition:

• Nitrogen and Boron-free

• structure = almost all C atoms

most common color:

• colorless, whitest color due to little-no light absorption across visible spectrum (highly valuable)

• also brown, pink, green

describe the type IIb diamond (composition/most common color).

composition:

• mostly C atoms, small amounts of Boron substituting for some C atoms

most common color:

• blue to grey, caused by absorption of most light except blue by boron impurities

*very rare/valuable, eg. Hope Diamond

identify the most common cause(s) of colorless diamonds.

no impurities; pure

• best achievable: D color, commanding premium prices

identify the most common cause(s) of blue to grey color diamonds.

boron impurities (eg. Hope Diamond)

identify most common cause(s) of yellow to orange color diamonds (*range of intensity to almost colorless)

Nitrogen impurities (eg. Tiffany diamond)

identify the most common cause(s) of pink-purple-red-cognac color diamonds.

deformation of crystal structure (hypothesized) (eg. Rob Red, Agra diamonds)

identify the most common cause(s) of green color diamonds.

natural irradiation (eg. Dresden Green diamond)

identify the most common cause(s) of black color diamonds.

abundant graphite and other opaque materials (inclusions) in the diamond (eg. Black Orlov)

identify the most common diamond treatments

• high pressure, high temp (HPHT) annealing

  • alters N atom arrangement, “heals” lattice vacancies, removes brown body color, or enhances existing yellow color

• glass-filling

  • fills fractures/flaws, improves overall clarity

• laser-drilling

  • reaches inclusions sealed from surface of the stone, followed by boiling acid bath

  • either bleaches or dissolves out the inclusion, then filled with glass

Identify the most common methods of creating synthetic diamonds.

• Chemical Vapor Deposition (CVD)

• High Pressure High Temperature Growth (HPHT)

• both produce diamonds large enough to be used as gemstones, almost indistinguishable from natural diamonds

What differentiates Type I from Type II diamond?

• Type I has nitrogen impurities, type II doesn’t

• Type I: N > 10ppm, Type II: N < 10ppm

Why are Type IIb diamonds so rare?

contain small amounts of Boron but no appreciable Nitrogen, creating blue/grey hue

Which of the physical properties of diamond might a geologist use to identify a rough diamond in the field?

Electrical conductivity

Which of the physical properties of diamond might a gemologist used to distinguish a cut diamond from some of its imitators

Hardness