Erythrite (also known as cobalt bloom or red cobalt) is a secondary hydrated cobalt-arsenic mineral that forms a complete series with annabergite, a hydrated nickel arsenate. The general formula of the two end members is (Co, Ni)3(AsO4)2路8H2O). Erythrite is monoclinic and usually occurs as secondary crusts or coating in crimson to pinkish red colors, as here seen. More rarely it forms thin prismatic or acicular (needle-like) crystals, the latter sometimes in radial arrangement. Actual width is 60 mm.