By heating a mixture of cobalt oxalate and sal-ammoniac in air, it is obtained in the form of minute hard octahedra, which are not magnetic, and are only soluble in concentrated sulphuric acid.
This solution, on standing, deposits octahedra of the composition CoC1 2.6NH 3.
It forms grey coloured octahedra of specific gravity 5.49 6 at 20° C., melting at 900° C.; it burns at a red heat, is insoluble in hydrochloric acid, but dissolves in aqua regia, and is also soluble in molten alkalis.
Many of them contain large octahedra of magnetite.
It crystallizes in octahedra isomorphous with stannic oxide.