Brassite

Brassite is a rare arsenate mineral with the chemical formula Mg(AsO₃OH)·4(H₂O). It was named brassite, in 1973, to honor French chemist Réjane Brasse, who first synthesized the compound. The type locality for brassite is Jáchymov of the Czech Republic.^[3]

Brassite
Brassite (white) accompanied by rösslerite
General
Category	Arsenate mineral
Formula	Mg(AsO3OH)·4(H2O)
IMA symbol	Bsi[1]
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	[2][3][4][5]

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.^[4]

Localities

Czech Republic:

• Jáchymov, Ore Mountains, Karlovy Vary Region, 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