Hypersthene

Hypersthene, also known as bronzite, was a gemstone usually cut cabochon.

Description
This semi-precious stone was brown and opaque (sometimes reddish or greenish) and contained silvery spangles. It was rare to find an unflawed piece larger than $1/2$ in (13 mm) across, and as a result the stone yielded small gemstones. A typical stone had a base value of 50 gp.