coquimbite

Coquimbite is a hydrated iron sulfate mineral with the chemical formula Fe2(SO4)3·9H2O. It is a relatively rare mineral, typically found in arid or semi-arid environments where iron-bearing rocks are exposed to weathering. Coquimbite commonly forms as a secondary mineral, resulting from the oxidation of iron sulfides such as pyrite.

The mineral typically occurs as small, acicular or prismatic crystals, often forming efflorescences or crusts on rock surfaces. Its color can range from pale yellow to violet, depending on the presence of impurities. Coquimbite is moderately soluble in water and has a vitreous to silky luster. It is known to be hygroscopic, meaning it readily absorbs moisture from the air.

Coquimbite was first described in 1830 from a locality in the Coquimbo Region of Chile, which is the source of its name. It is a member of the hexahydrite group of sulfates. While not economically significant, coquimbite is of interest to mineral collectors and geologists studying weathering processes and secondary mineral formation in arid climates. It can also be an indicator of acidic conditions.