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Composition:
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C (carbon)
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Crystallographic Class:
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Cubic -- hexoctahedral (highest of the symmetries)
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Space Group:
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Fd3m -- a = 3.57 A (cell edge)
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Common Forms {indices}:
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F Octahedron {111}, cube {100}, dodecahedron {110},
rounded variations
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Twins:
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Spinel-law common, yielding the flat triangular "macle"
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Hardness:
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10 Mohs' scale, 56-115 Knoop hardness number (GPa),
10,000 Brooks identer scale;
octahedral face hardest, cube face softest
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Cleavage:
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Excellent parallel to octahedron face -- {111}
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Density:
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3.51 g/cm3 (or specific gravity = 3.51)
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Luster:
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Adamantine (diamond provides the definition for this kind of luster)
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Colors:
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Colorless, yellow, blue, and many others
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Refractive Index:
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2.4175 (in the yellow light of a sodium lamp)
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Dispersion:
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Large (0.044), leading to rainbow colors on refraction
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Optical Transmission:
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Transparent over broad spectrum of the
electromagnetic spectrum; an excellent material for
optical windows
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Thermal Conductivity:
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Superb -- 5-25 Watts/centimeter-degreesC (at 300 K); 4 times
greater than copper, an excellent thermal conductor
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Electrical Conductivity:
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0 to ~ 100 ohm-cm (resistivity at 300 K) -- an insulator
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