Majorite
Garnet mineral / From Wikipedia, the free encyclopedia
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Majorite is a type of garnet mineral found in the mantle of the Earth. Its chemical formula is Mg3(MgSi)(SiO4)3. It is distinguished from other garnets in having Si in octahedral as well as tetrahedral coordination. Majorite was first described in 1970 from the Coorara Meteorite of Western Australia and has been reported from various other meteorites in which majorite is thought to result from an extraterrestrial high pressure shock event.[2][3] Mantle derived xenoliths containing majorite have been reported from potassic ultramafic magmas on Malaita Island on the Ontong Java Plateau Southwest Pacific.[6]
Quick Facts General, Category ...
Majorite | |
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General | |
Category | Nesosilicates |
Formula (repeating unit) | Mg3(MgSi)(SiO4)3 |
IMA symbol | Maj[1] |
Strunz classification | 9.AD.25 |
Crystal system | Cubic |
Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m) |
Space group | Ia3d or tetragonal I41/a for pure MgSiO3 |
Unit cell | a = 11.52 Å; Z = 8 |
Identification | |
Color | Purple, pale yellowish brown, colorless |
Crystal habit | Microcrystalline aggregates; acicular to equant grains in narrow veinlets |
Cleavage | None |
Mohs scale hardness | 7–7.5 |
Luster | Vitreous |
Diaphaneity | Semitransparent |
Specific gravity | Measured at about 4; 3.51 (calculated for pure MgSiO3) |
Optical properties | Isotropic |
Refractive index | n = 1.87 – 1.92 (calculated) |
Birefringence | slight |
References | [2][3][4][5] |
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