Chemistry:Felsőbányaite

Felsőbányaite
Felsöbanyaite as white spherules. Roadcut near Sant Marti dels Castells (Lérida) Spain
General
Category	Sulfate mineral
Formula (repeating unit)	Al4(SO4)(OH)10·4H2O
Strunz classification	7.DD.05
Crystal system	Monoclinic
Crystal class	Sphenoidal (2) (same H-M symbol)
Space group	P21
Unit cell	a = 13.026 Å, b = 10.015 Å, c = 11.115 Å; β = 104.34°; Z = 4
Identification
Color	White to pale yellow, pale brown
Crystal habit	Globular masses, minute rhombic crystals
Cleavage	Distinct to good on {010} and {100}
Mohs scale hardness	1.5
|re|er}}	Vitreous, pearly on cleavage surfaces
Diaphaneity	Semitransparent
Specific gravity	2.33
Optical properties	Biaxial (+)
Refractive index	n = 1.515–1.540
References

Felsőbányaite or basaluminite is a hydrated aluminium sulfate mineral with formula: Al₄(SO₄)(OH)₁₀·4H₂O. It is a rare white to pale yellow mineral which typically occurs as globular masses and incrustations or as minute rhombic crystals. It crystallizes in the monoclinic crystal system.

It occurs as a weathering product under acidic conditions associated with pyrite or marcasite decomposition. Associated minerals include hydrobasaluminite, hydroargillite, meta-aluminite, allophane, gibbsite, gypsum and aragonite.

Felsőbányaite was first described in 1853 for an occurrence in the Baia Sprie mine, Baia Sprie (Felsőbánya), Maramureș County, Romania, and named for the locality. The mineral name basaluminite was used for an occurrence of the same mineral in England in 1948 and discredited by the International Mineralogical Association (IMA) in 2006.