Note: Do not rely on this information. It is very old.
Gahnite consists of an aluminate of zinc, which crystallises in the regular system. usually in octahedra, resembling the spinels (q.v.). It varies in colour from green to blue-black or brown; has a specific gravity of 7.8, and hardness 4.5. It frequently contains, besides its chief constituents, iron or manganese and sometimes magnesium. It occurs in a few localities in Sweden, Bavaria, and America, but not very plentifully.