(n.) A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). opal. Retrieved September 21, 2026, from http://smartdefine.org/opal/definitions/2038941 |
| Chicago | Webster's. 2011. "opal" http://smartdefine.org/opal/definitions/2038941 (accessed September 21, 2026). |
| Harvard | Webster's 2011, opal, Smart Define, viewed 21 September, 2026, <http://smartdefine.org/opal/definitions/2038941>. |
| MLA | Webster's. "opal" 27 May 2011. Web. 21 September 2026. <http://smartdefine.org/opal/definitions/2038941> |