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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]
Ceylonite, named for the island of Ceylon, is a ferroan spinel with Mg:Fe from 3:1 and 1:1, and little or no ferric iron. Pleonaste is named from the Greek for 'abundant,' for its many crystal forms, and is distinguished chemically by low Mg:Fe ratios of approximately 1:3. It is sometimes used as a gemstone. [2]
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.
Before buying any old gem, though, keep reading to uncover the 25 most popular gemstones—and their meanings. Agate “Agate is earthy, warm and rich,” Salzer says, noting that it exists in ...
The Spinel of the Great Imperial Crown (Russian: Шпинель Большой императорской короны) or Menshikov Ruby [1] (Russian: Рубин Меншикова) is a historical gemstone, a red spinel which tops the Great Imperial Crown of Russia from the 18th century to the present day.
[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. [6]
Galaxite is the manganese (Mn) rich endmember of the aluminium (Al) series of the spinel group. Divalent iron (Fe) and magnesium (Mg) readily substitute for the manganese in the crystal structure. Trivalent iron may also substitute for the aluminium. Thus, reflecting most natural samples, the formula may be better represented as (Mn,Fe 2+,Mg ...
Chromite is a part of the spinel group, which means that it is able to form a complete solid solution series with other members in the same group. These include minerals such as chenmingite (FeCr 2 O 4 ), xieite (FeCr 2 O 4 ), magnesiochromite (MgCr 2 O 4 ) and magnetite (Fe 2+ Fe 3+ 2 O 4 ).