Opal
From BiblePortal Wikipedia
Webster's Dictionary [1]
(n.) A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity.
The Nuttall Encyclopedia [2]
A variety of quartz, of which the finest kind, precious opal, is translucent, with blue or yellow tint, and when polished with a convex sur face shows an admirable play of colours; it is found chiefly at Cerwenitza, Austria.
