A monoclinic mineral, 2(Co₃(AsO₄)₂.8H₂O) ; forms a series with annbergite and with hoernesite; occurs in soft pink to crimson crystals, globular or reniform masses, or earthy encrustations as a weathering product of cobalt ores in the oxidized parts of nickelarsenic- silver-bearing veins; used as ore indicator for cobalt and possibly silver.