Galaxite
(repeating unit)MnAl2O4 IMA symbol Glx[1] Strunz classification 4.BB.05 Crystal system Cubic Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m) Space group Fd3m (no. 227) Unit cell a = 8.271 Å; Z = 8 Identification Color Black, red-brown, red to yellow Crystal habit Octahedra and rounded grains and exolution blebs Twinning Spinel law with {111} as both twin and composition plane Cleavage Indistinct to none Fracture Conchoidal to irregular Tenacity Brittle Mohs scale hardness 7.5 Luster Vitreous Streak Red-brown Diaphaneity Opaque; may be translucent in thin section Specific gravity 4.234 Optical properties Isotropic Refractive index n = 1.923 Other characteristics weakly to moderately magnetic References [2][3][4]
H-M symbol: (4/m 3 2/m)
Galaxite, also known as 'mangan-spinel' is an isometric mineral belonging to the spinel group of oxides with the ideal chemical formula Mn2+Al2O4.[5]
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,Fe2+,Mg)(Al,Fe3+)2O4.[3]
Galaxite generally occurs as small granular aggregates with a red-brownish tone. It has a vitreous luster and leaves a brownish-red streak. It is rated 7.5 on the Mohs Scale.[3]
It was first described in 1932 for an occurrence at Bald Knob, Alleghany County, North Carolina near its namesakes, the town of Galax, Virginia, named after the plant galax or wandflower which grows in the area.[3][4]
It occurs in carbonate-rich metamorphosed manganese ore deposits. It occurs associated with alleghanyite, rhodonite, sonolite, spessartine, tephroite, kutnohorite, manganhumite, jacobsite, kellyite and alabandite in the Bald Knob area. Associated minerals include katoptrite, magnetite, manganostibite, magnussonite, tephroite, manganhumite and manganosite in the Brattfors mine area of Nordmark, Värmland, Sweden.[3]
It is sometimes used as a gemstone.[6]
References
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Mindat.org
- ^ a b c d e Handbook of Mineralogy
- ^ a b Webmineral data
- ^ "IMA Mineral List with Database of Mineral Properties".
- ^ Tables of Gemstone Identification By Roger Dedeyne, Ivo Quintens, p.282
- IMA Database - Galaxite
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