automalite

A mineral called by Hauy, spinelle zincifere. it is classed with the spinel ruby. it occurs imbedded in talcky slate; the color, a dark green. It is crystallized in regular octahedrons, or in tetrahedrons with truncated angles. It is harder than quartz, but not so hard as spinel. It is sometimes called gahnite, from Gahn, its discoverer.