| Cleavage | . | ||||||||||||||||
| (111) - perfect - parallel to the (111) close packed layers | . | ||||||||||||||||
| . | |||||||||||||||||
| Crystal habit | . | ||||||||||||||||
| Predominately octahedral, less commonly dodecahedral, rarely cubic, | . | ||||||||||||||||
| occasionally tetrahedral; twinning on (111) very common. | . | ||||||||||||||||
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| The graphite and diamond polymorphs of carbon is a classic illustration of the | . | ||||||||||||||||
| effect that the geometry of the atomic packing has on the chemical and physical | |||||||||||||||||
| properties of matter. In its graphite form carbon is one of the softest natural | |||||||||||||||||
| materials known and it is a good lubricant. In contrast, in its diamond form, it is the | |||||||||||||||||
| hardest natural material known and it is an excellent abrasive. The tetrahedral | |||||||||||||||||
| arrangement of the carbon atoms in diamond is primarily responsible for its | |||||||||||||||||
| hardness due to the omni-triangulated nature of its structure. Carbon's extreme | |||||||||||||||||
| polymorphism is the result of the different conditions under which its crystals are | |||||||||||||||||
| formed. It is only when carbon is subjected to extremes of temperature and pressure | |||||||||||||||||
| that it morphs into the diamond structure. | |||||||||||||||||
| . | |||||||||||||||||
| Only a few native elements exist in pure form in their natural state on earth (Au, | |||||||||||||||||
| Ag, Cu, Hg, Pb, Pt, Sn, Fe, C, S, Sb, As, Bi, and the inert gases). The rest must be | |||||||||||||||||
| extracted, refined, and crystallized from their ore minerals. The following section | |||||||||||||||||
| describes the geometry and symmetry of minerals in terms of their topology. | |||||||||||||||||
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Back to Knowhere |
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Page 37 - Structure matters - Diamond structure elements |
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