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The chief of these are the garnets, crystallising in the cubic system, and anhydrous. The garnet is usually in the form of a rhombic dodecahedron, or as a trisoctahedron (called also sometimes an icosatetrahedron), or a mixture of the two, though the stones appear in other cubic forms. In hardness they vary from [...] Group C. Stones whose specific gravity lies between 3.50 and under 3.70. Pyrope (average) 3.682 Chrysoberyl 3.689 and occasionally to 3.752 Spinel 3.614 ” 3.654 Kyanite 3.609 ” 3.688 Hessonite 3.603 ” 3.651 Diamond 3.502 ” 3.564 Topaz 3.500 ” 3.520 |
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