Adamantine Spar, a genus of earths, of three varieties. The color of the first is gray, with shades of brown or green; the form when regular, a hexangular prism, two sides large and four small, without a pyramid; its surface striated, and with a thin covering of white mica, interspersed with particles of red felspar; its fracture, foliaceous and sparry. The second variety is whiter, and the texture more foliaceous. The third variety is of a reddish brown color. This stone is very hard, and of difficult fusion.

A variety of corrundum.