KFe₃(SO₄)₂(OH)₆

This sample of jarosite is displayed in the Smithsonian Museum of Natural History. Jarosite is a sulfate mineral of iron and potassium with the composition KFe₃(SO₄)₂(OH)₆. The sample at left is about 8 cm across and is from Santa Eulalia, Chihuahua, Mexico.