A phosphate CuAl6 (PO4)4(OH)84–5H2O; sp. gr. 2.60–2.91; hardness 5.0–6.0; triclinic; sky-blue to blue-green; white or greenish streak; waxy lustre; crystals very rare, normally occurs massive, granular to cryptocrystalline, or as encrusting masses; conchoidal fracture; occurs in veins in association with aluminous, igneous, or sedimentary rocks that have undergone alteration. Finer varieties are used for semi-precious stones.