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Felsöbanyaite Soria.jpg
Felsöbanyaite as white spherules. Roadcut near Sant Marti dels Castells (Lérida) Spain
CategorySulfate mineral
(repeating unit)
Strunz classification7.DD.05
Crystal systemMonoclinic
Crystal classSphenoidal (2)
(same H-M symbol)
Space groupP21
Unit cella = 13.026 Å, b = 10.015 Å,
c = 11.115 Å; β = 104.34°; Z = 4
ColorWhite to pale yellow, pale brown
Crystal habitGlobular masses, minute rhombic crystals
CleavageDistinct to good on {010} and {100}
Mohs scale hardness1.5
LusterVitreous, pearly on cleavage surfaces
Specific gravity2.33
Optical propertiesBiaxial (+)
Refractive indexn = 1.515–1.540

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.[2][1]

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.[2]

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.[1] 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.[3]