Arsenate minerals
Arsenate minerals usually refer to the naturally occurring orthoarsenates, possessing the (AsO4) anion group and, more rarely, other arsenates with anions like AsO3(OH) (also written HAsO4) (example: pharmacolite Ca(AsO3OH)2H2O) or (very rarely) [AsO2(OH)2] (example: andyrobertsite). Arsenite minerals are much less common. Both the Dana and the Strunz mineral classifications place the arsenates in with the phosphate minerals.