Brassite

Brassite
Brassite (white) accompanied by rösslerite
General
Category	Arsenate mineral
Formula (repeating unit)	Mg(AsO3OH)·4(H2O)
Strunz classification	8.CE.15
Dana classification	39.01.07.01
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pbca
Unit cell	a = 7.472 Å, b = 10.891 Å, c = 16.585 Å; Z = 8
Identification
Color	White
Crystal habit	Cryptocrystalline crusts
Cleavage	{001} Perfect
Fracture	Irregular/uneven, splintery
Tenacity	Brittle
Luster	Silky, dull, earthy
Streak	White
Diaphaneity	Translucent
Specific gravity	2.28
Optical properties	Biaxial (+)
Refractive index	nα = 1.531 nβ = 1.546 nγ = 1.562
Birefringence	0.031
Pleochroism	Non-pleochroic
2V angle	80°
Dispersion	r < v moderate
Solubility	+++ HCl, + H2O
References

Brassite is a rare arsenate mineral with the chemical formula Mg(AsO₃OH)·4(H₂O). It was named brassite, in 1973, to honor French chemist R`ejane Brasse, who first synthesized the compound. The type locality for brassite is Jáchymov of the Czech Republic.

It occurs as an alteration of magnesium carbonate minerals by arsenic bearing solutions. It occurs associated with pharmacolite, picropharmacolite, weilite, haidingerite, rauenthalite, native arsenic, realgar and dolomite.

Localities

Czech Republic:

• Jáchymov (St Joachimsthal), Jáchymov, Krušné Hory Mts (Erzgebirge), Karlovy Vary Region, Bohemia, Czech Republic

France:

• Salsigne mine, Salsigne, Mas-Cabardès, Carcassonne, Aude, Languedoc-Roussillon, France
• Villanière (slag locality), Salsigne, Mas-Cabardès, Carcassonne, Aude, Languedoc-Roussillon, France

Germany:

• Wilhelm Mine (Wechselschacht), Bauhaus, Richelsdorf District, Hesse, Germany
• Ore dumps, Richelsdorf Smelter, Süss, Richelsdorf District, Hesse, Germany