A rare hydrous zinc arsenate, Zn₂(AsO₄)(OH) , occurring granular or in crusts and crystallizing in the orthorhombic system. Weakly radioactive; variable color--yellowish, greenish, or violet, rarely colorless or white; found in the oxidized zone of zinc orebodies. Associated with smithsonite, calcite, malachite, hemimorphite, limonite, and azurite. Small amounts of uranium have been found in some specimens of adamite.