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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]
The heterogeneity of spinel group members varies based on composition with ferrous and magnesium based members varying greatly as in solid solution, which requires similarly sized cations. However, ferric and aluminium based spinels are almost entirely homogeneous due to their large size difference. [9]
In aluminium alloys containing magnesium, magnesium oxides (MgO), cuboids (MgAl 2 O 4-cuboid) and metallurgical spinel (MgAl 2 O 4-spinel) can form. They result from the reaction between magnesium and oxygen in the melt. More of them will form with time and temperature. Spinel can be highly detrimental because of its big size and high hardness.
Magnesium aluminate spinel (MgAl 2 O 4) is a transparent ceramic with a cubic crystal structure with an excellent optical transmission from 0.2 to 5.5 micrometers in its polycrystalline form. Optical quality transparent spinel has been produced by sinter/HIP, hot pressing, and hot press/HIP operations, and it has been shown that the use of a ...
Magnesium aluminide is an intermetallic compound of magnesium and aluminium. Common phases (molecular structures) include the beta phase (Mg 2 Al 3 ) and the gamma phase (Mg 17 Al 12 ), which both have cubic crystal structures.
The accessory minerals can be useful for estimating the depth of formation of the peridotite. For example, the aluminium in lhertzolite is present as plagioclase at depths shallower than about 20 kilometers (12 mi), while it is present as spinel between 20 km and 60 kilometers (37 mi) and as garnet below 60 km. [24]
All red gemstones used to be referred to as rubies or "balas rubies". It was not until 1783 that spinels were chemically differentiated from rubies. [5] They both contain aluminium and oxygen, and both derive their colour from chromium(III), but the spinel crystal also contains magnesium, which rubies lack.
This list includes those recognised minerals beginning with the letter M.The International Mineralogical Association is the international group that recognises new minerals and new mineral names; however, minerals discovered before 1959 did not go through the official naming procedure, although some minerals published previously have been either confirmed or discredited since that date.