galaxite
{{infobox mineral
| name = Galaxite
| category = Oxide minerals
Spinel group
Normal Spinel structural group
| image = Galaxite-Jacobsite-Wiserite-697074.jpg
| alt =
| caption = Galaxite from the Kaso mine, Japan
| formula = {{chem2|MnAl2O4}}
| molweight =
| strunz = 4.BB.05
| dana =
| system = Cubic
| class = Hexoctahedral (m{{overline|3}}m)
H-M symbol: (4/m {{overline|3}} 2/m)
| symmetry = Fd{{overline|3}}m (no. 227)
| unit cell = a = 8.271 Å; Z = 8
| color = Black, red-brown, red to yellow
| colour =
| 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 = 7.5
| luster = Vitreous
| streak = Red-brown
| diaphaneity = Opaque; may be translucent in thin section
| gravity = 4.234
| density =
| polish =
| opticalprop = Isotropic
| refractive = n = 1.923
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| other = weakly to moderately magnetic
| prop1 =
| prop1text =
| references = [http://www.mindat.org/min-1639.html Mindat.org ][http://rruff.geo.arizona.edu/doclib/hom/galaxite.pdf Handbook of Mineralogy][http://webmineral.com/data/Galaxite.shtml Webmineral data]
}}
Galaxite, also known as 'mangan-spinel' is an isometric mineral belonging to the spinel group of oxides with the ideal chemical formula {{chem2|Mn^{2+}Al2O4}}.{{Cite web|url=http://rruff.info/ima/|title = IMA Mineral List with Database of Mineral Properties}}
It is sometimes used as a gemstone.Tables of Gemstone Identification By Roger Dedeyne, Ivo Quintens, p.282
Occurrence
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.
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.
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.
Composition
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 {{chem2|(Mn,Fe^{2+},Mg)(Al,Fe^{3+})2O4}}.
References
{{Reflist}}
- [http://rruff.info/ima/ IMA Database - Galaxite]
Category:Manganese(II) minerals
Category:Minerals in space group 227
Category:Minerals described in 1932
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