Noah Webster's Dictionary (n.) A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity.

Multi-Version Concordance Opal (2 Occurrences) Exodus 28:19 and the third row, an opal, an agate, and an amethyst; (DBY YLT) Exodus 39:12 and the third row, an opal, an agate, and an amethyst; (DBY YLT)