jarosite

Physical properties

Habit: minute pseudocubic crystals or tabular, also granular, massive, earthy cryptocristalline crust and coatings.
Color: ocherous, amber-yellow or dark brown.
Diaphaneity: opaque.
Luster: subadamantine to vitreous or resinous.
Streak: pale yellow.
Fracture: uneven to conchoidal.
Cleavage: distinct (0001).
Other: Pyroelectric.
Chemical: insoluble in water but dissolves in HCl.
Occurrence: widespread secondary mineral as encrustation and coating in the oxidizing zone of sulfidic ore deposits along with limonite and goethite. Forms from the aerobic alteration of pyrite.