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Demantoid is the green gemstone variety of the mineral andradite, a member of the garnet group of minerals. Andradite is a calcium- and iron-rich garnet. The chemical formula is Ca 3 Fe 2 (SiO 4) 3 with chromium substitution as the cause of the demantoid green color. Ferric iron is the cause of the yellow in the stone.
A polished almandine stone . Carbuncle (/ ˈ k ɑːr b ʌ ŋ k əl /) is another name for a deep red almandine gemstone that has been cut with a smooth, convex face in a method called cabochon. [1] Traditionally, the term referred to any red gemstone, most often a red garnet. [2] Carbuncles and their chimeras have spanned three millennia.
Garnet sand is also used for water filtration media. As an abrasive, garnet can be broadly divided into two categories; blasting grade and water jet grade. The garnet, as it is mined and collected, is crushed to finer grains; all pieces which are larger than 60 mesh (250 micrometers) are normally used for sand blasting.
Asterism is generated by reflections of light from twin-lamellae or from extremely fine needle-shaped acicular inclusions within the stone's crystal structure. [1] A common cause is oriented sub-microscopic crystals of rutile within the gem mineral. It occurs in rubies, sapphires, garnet, diopside, and spinel when a cabochon is cut from a ...
It is a nesosilicate, with formula Ca 3 Fe 2 Si 3 O 12. Andradite includes three varieties: Colophonite: a historical variety found in the Scandinavian islands, brownish or reddish in color, often opaque or translucent. [6]: 61 Demantoid: Vivid green in color, one of the most valuable and rare stones in the gemological world. [7]
Uvarovite is a chromium-bearing garnet group species with the formula: Ca 3 Cr 2 (Si O 4) 3. It was discovered in 1832 by Germain Henri Hess who named it after Count Sergei Uvarov (1765–1855), a Russian statesman and amateur mineral collector. [2] It is classified in the ugrandite group alongside the other calcium-bearing garnets andradite ...