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[4] [5] As such, it is the only gemstone to have been initially identified from a faceted stone. Most pieces of the gem, prior to Taaffe, had been misidentified as spinel . For many years afterwards, it was known only in a few samples, and it is still one of the rarest gemstone minerals in the world.
Polyhedral representation of spinel MgAl 2 O 4. Spinel (/ s p ɪ ˈ n ɛ l, ˈ s p ɪ n əl / [7]) is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl 2 O 4 in the cubic crystal system. Its name comes from the Latin word spinella, a diminutive form of spine, in reference to its pointed crystals. [5]
An example of an inverse spinel is Fe 3 O 4, if the Fe 2+ (A 2+) ions are d 6 high-spin and the Fe 3+ (B 3+) ions are d 5 high-spin. In addition, intermediate cases exist where the cation distribution can be described as (A 1− x B x )[A x ⁄ 2 B 1− x ⁄ 2 ] 2 O 4 , where parentheses () and brackets [] are used to denote tetrahedral and ...
By 1910, Verneuil's laboratory had expanded into a 30-furnace production facility, with annual gemstone production by the Verneuil process having reached 1,000 kg (2,200 lb) in 1907. By 1912, production reached 3,200 kg (7,100 lb), and would go on to reach 200,000 kg (440,000 lb) in 1980 and 250,000 kg (550,000 lb) in 2000, led by Hrand ...
The garnet group has a general formula of X 3 Y 2 (SiO 4) 3, where X is a large eight-fold coordinated cation, and Y is a smaller six-fold coordinated cation. There are six ideal endmembers of garnet, split into two group. The pyralspite garnets have Al 3+ in the Y position: pyrope (Mg 3 Al 2 (SiO 4) 3), almandine (Fe 3 Al 2 (SiO 4) 3), and ...
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Samarian Spinel, the world's largest spinel; Menshikov Ruby, the world's second largest spinel set on top of the Great Imperial Crown of Russia; Timur Ruby, believed to be a ruby until 1851, hence its name; Black Prince's Ruby, the famous spinel mounted on the Imperial State Crown of the United Kingdom
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