Class : Sulfates, chromates, molybdates
    Subclass : Hydrated sulfates
    Crystal system : Monoclinic
    Chemistry : CuAl₄SO₄(OH)₁₂ 3H₂O
    Rarity : Rare to uncommon

Chalcoalumite is a hydrated sulfate of copper and aluminum. It is a secondary mineral of the oxidation zones of copper deposits. It owes its name to its chemical composition : from the Greek khalcos (copper) and the Latin alumen (alum). It essentially forms fibrous botryoidal encrustations, sometimes small triangular, finely lamellar crystals grouped into small spherules, of a pale bluish green to blue or blue-gray color. It transforms into copper-bearing gibbsite by dehydration.

Main photo : Chalcoalumite from Holbrook Mine, Arizona, USA © Rob Lavinsky

A twin is known to have a re-entrant angle, but is difficult to identify.

No fakes identified for this mineral species, confusion with chrysocolla or gibbsite may occur.