Köttigite

Köttigite is a rare hydrated zinc arsenate which was discovered in 1849 and named by James Dwight Dana in 1850 in honour of Otto Friedrich Köttig (1824 - 1892), a German chemist from Schneeberg, Saxony, who made the first chemical analysis of the mineral. It has the formula Zn₃(AsO₄)₂·8H₂O and it is a dimorph of metaköttigite, which means that the two minerals have the same formula, but a different structure: köttigite is monoclinic and metaköttigite is triclinic. There are several minerals with similar formulae but with other cations in place of the zinc. Iron forms parasymplesite Fe₃(AsO₄)₂·8H₂O; cobalt forms the distinctively coloured pinkish purple mineral erythrite Co₃(AsO₄)₂·8H₂O and nickel forms annabergite Ni₃(AsO₄)₂·8H₂O. Köttigite forms series with all three of these minerals and they are all members of the vivianite group.