Hardness: 5 - 6.5
Specific Gravity: 2.15
Refraction Index: 1.45
Species: Silica Gel
Treatment: None
Care: Never clean ultrasonically, hot water or steam clean.

Opal is one of the October birthstones.  The name opal comes from the Greek Opallos, meaning "to see a change of color."  It is a formation of non-crystalline silica gel that seeped into crevices in the sedimentary strata. Through time and nature's heating the gel hardened into the form of opals.  Beliefs associated the powers of foresight and prophecy, hope and purity.