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.
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, 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
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