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 Characteristics |
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 Structure and property |
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 Family: diamond |
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Chemical composition: C, carbon |
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Hardness: 10 Mohs' scale, 56-115 Knoop hardness
number (GPa), 10,000 Brooks identer scale. |
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Crystallography: Isometric. Crystals sometimes sharp
octahedral, rhombic dodecahedral, cubes, twinning, plates, and combinations with other forms. Crystals
modified often rounded and distinguished by the presents of triangular shaped pits on the faces of the
octahedral shaped crystals. These trigons were once thought to be the result of etching are now believed
to be part of the growth process. |
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Luster: Adamantine (diamond provides the definition for
this kind of luster). |
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Cleavage: Excellent, parallel to octahedron face, four
directions. |
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Density: 3.51 g/cm3,
or specific gravity = 3.51 (3.51 at
3.53). |
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Refractive Index:
2.4175 in the yellow light of a sodium lamp.
(2.417 at 2.419) |
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Birefringence: none |
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Pleochroism: none |
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Dispersion: Large
(0.044), leading to rainbow colours on refraction. |
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Optics: Isotropic. Index very constant. N =
2.417. |
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Thermal Conductivity: Superb. 5-25 Watts/centimeter-degreesC
(at 300 K). 4 times greater than copper, an excellent thermal conductor. |
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Electrical Conductivity: 0 to ~ 100 ohm-cm (resistivity
at 300 K), an insulator. |
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Optical Transmission: Transparent over broad spectrum of
the electromagnetic spectrum. An excellent material for optical windows. |
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| Colours : |
Colourless |
Blue |
Green |
Yellow |
Pink |
Red |
Orange |
Brown |
Black |
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| Definitions of terms |
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Index of refraction |
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 The index of refraction is defined as the
speed of light in vacuum divided by the speed of light in the medium. |
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Birefringence |
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A single light
ray is split into two rays as it is transmitted into uniaxial and
biaxial minerals. The two rays travel at different velocities
through the mineral, which is why uniaxial minerals have two indices
of refraction (nw and ne). The difference between the two indices of
refraction is called birefringence. |
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Pleochroism |
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The splitting of light into
two light rays may result in an effect called pleochroism in some
coloured transparent uniaxial and biaxial minerals. Pleochroism is
produced because the two rays of light are differencially absorbed as
they pass through the coloured anisotropic mineral. Because the
absorption is different for the two light rays, the wavelengths and
colours of the two light rays are different when they emerge from the
crystal. The colour of ruby and sapphire (uniaxial corundum) is
caused in part by a blending of the two colours. Biaxial minerals, or
those that crystallize in the orthorhombic, monoclinic, and triclinic
crystal systems, can have three distinct colours. Tiny crystals of
biaxial ivaite, the black mineral in the photograph to the left, is
strongly pleochroic (yellow, dark brown, and dark green). |
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Dispersion |
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The index of refraction of
an isometric mineral is not the same for all wavelengths of light.
When a ray of white light travels from air into a triangular glass
prism, the light not only bends but it also is separated into its
component colours or wavelengths, the colours of the spectrum. The
violet light is bent slightly more than the red, for instance, because
it travels more slowly through the glass. As the light emerges from
the prism the colours separate even more. This phenomenon, called
dispersion, can be observed in some minerals such as diamond.
Jewelers refer to this characteristic in gemstones as fire. The next
time you look at a diamond, observe the rainbow of colours caused by
the splitting of white light into its component wavelengths. |
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For more information on gemstones, we invite
you to visit some sites:
Gem Hut: serving the Internet with fine and rare
coloured gemstones from around the world.
Bob's Rock Shop: is a mineral 'zine with many
links to other rockhound or mineral topics.
Mineralogical Association of Canada: in
addition to regular bi-monthly articles on minerals, publishes the IMA listing of approved
minerals in their journal, "The Canadian Mineralogist." You can browse the abstracts
on-line. |
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0.47 carat E-VVS1 |
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0.67 carat H-IF |
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1.92 carat E-IF |
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1.37 carat D-SI1 |
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0.28 carat F-VVS2 |
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| Price: £ 1,124 |
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| Price: £ 1,402 |
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| Price: £ 13,510 |
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| Price: £ 4,995 |
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| Price: £ 307 |
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