EOSC 118 Lecture Notes - Lecture 9: Moissanite, Nanocrystalline Material, Thermal Conductivity
4 Dec 2017
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Document Summary
Diamond = pure carbon in crystalline structure w/ cubic symmetry + perfect octahedral cleavage. Cubic/isometric symmetry = all axes = same length + 90 degrees to each other, and unit cells = cubes/tetrahedrons made of covalently bonded c. Most common habit = octahedral, but dodecahedron, cubes, macles (tabular), twinned + mixes also possible. Polycrystalline/diamond aggregates also possible, are harder than monocrystalline specimens. Knowledge of diamond"s weakness/cleavage required to cut stones + grind facets red line = cleavage = where bonds are furthest apart/weakest, black cube = unit cell. [111] = diamond"s planes which display perfect cleavage. Ranks 10 on mohs hardness scale, high durability, high refractive index + great dispersion. Dispersion = splitting light into colours of rainbow. However, application of nanocrystalline diamond onto imitations have caused problems in identification of gems recently. Also repels water + sticks slightly to grease, and some will also fluoresce. High thermal but low electrical conductivity makes diamonds distinctive.
