Chrysolite

Fran. Rueus[…]say as much of the chrysolite, a friend of wisdome, an enemy to folly.

And before he died, Taran-Ish had scrawled upon the altar of chrysolite with coarse shaky strokes the sign of DOOM.

A piece of marigold or bay leaf was imbedded in the metal, and over it a carbuncle or chrysolite was placed.