alunogen

alunogen, a sulfate mineral formed by sulfate solutions that attack aluminous minerals; alunogen is hydrated aluminum sulfate, formulated Al₂(SO₄)₃17H₂O. It typically occurs as an efflorescence or crevice filling in pyrite-containing coal formations, shales, or slates, as well as in the gossan (weathered capping) of sulfide ore deposits and in volcanic fumarole deposits. In older literature, alunogen and other hairlike sulfate minerals were called Haarsalz (“hair salts”). For detailed physical properties, see sulfate mineral (table).