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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]
Inverse spinel structures have a different cation distribution in that all of the A cations and half of the B cations occupy octahedral sites, while the other half of the B cations occupy tetrahedral sites. 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 2016, the American Gem Trade Association and Jewelers of America added spinel as an additional birthstone for August. [6] Britain's National Association of Goldsmiths created its own standardized list of birthstones in 1937. [7] In 2021, Japanese industry associations added ten new types of birthstones. [8]
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. [6] Since 2002, the International Mineralogical Association-approved name for taaffeite as a mineral is magnesiotaaffeite-2N'2S.
The Greek name amethystos alludes to the popular belief that amethyst prevented intoxication; as such, drinking vessels were made of amethyst for festivities, and carousers wore amulets made of it to counteract the action of wine. [6] The amethyst is a brilliant transparent stone of a purple color and varies in shade from violet purple to rose.
Although other minerals such as tourmaline, scapolite, corundum, spinel and quartz can form "cat's eye" stones similar in appearance to cymophane, the jewelry industry designates these stones as "quartz cat's eyes", or "ruby cat's eyes" and only chrysoberyl can be referred to as "cat's eye" with no other designation. [citation needed]
In geology and mineralogy, a mineral group is a set of mineral species with essentially the same crystal structure and composed of chemically similar elements. [1]Silicon-oxygen double chain in the anions of amphibole minerals.
Ruby spinel; List of ruby misnomers. Adelaide ruby (garnet) Arizona Ruby (garnet) American ruby (garnet) and (quartz) Sapphire. Padparadscha sapphire - dab - Padparadschah sapphire; Hope sapphire; Water sapphire; Natural Sapphire; Yogo sapphire; List of sapphire misnomers. Oriental amethyst a misnomer for corundum.
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