Alunite

Alunite is a mineral composed mainly of potassium aluminum sulfate, with the chemical formula KAl₃(SO₄)₂(OH)₆. It typically forms as a secondary mineral in volcanic and hydrothermal environments, often in areas with acidic, sulfate-rich waters. Alunite appears as dull, earthy, or crystalline crusts that can range in color from white and yellow to pink or reddish-brown. It has Historical significance because it was historically used in the production of alum for mordanting textiles. Geologically, alunite signals the past presence of acidic, sulfate-rich fluids and can be studied to understand mineral deposits or hydrothermal activity.