Opal Rough Specimen

OPAL

HISTORY, NAME, LOCALITIES: Opal has been a valuable gemstone since antiquity.  The name, pronounced OH-pul, stems from the Latin opalus, or “opal,” which in turn is derived from the Sanskrit upala, meaning “stone” or “jewel.”  Opal is collected in Australia, Mexico, Honduras, Italy, Slovakia, Ethiopia, and the United States (Nevada, Oregon, Idaho).

MINERALOGY, PROPERTIES, OCCURRENCE: Opal [hydrous silicon dioxide, SiO₂·nH₂O] is not technically a mineral because it lacks a crystal structure and definite chemical composition.  Opal is an amorphous, layered, solidified, colloidal silica gel that is correctly classified as a mineraloid (a natural, mineral-like material).  It has a Mohs hardness of 5.5-6.0, vitreous-to-dull luster, and a specific gravity of 1.9-2.3.  Opal is translucent and usually colorless or white, but it can also have a wide range of pale hues.  Opalescent varieties exhibit a rich play of internal colors that can span the entire spectral range.  As a low-temperature silicate, opal develops as amorphous fracture and cavity fillings in sedimentary and volcanic environments when silica gels solidify slowly under specific conditions of temperature and pressure.

METAPHYSICAL PROPERTIES, LORE, USES:  Precious opal, a valuable gemstone because of its brilliant opalescence or “fire,” is cut into cabochon gems.  Australia is the largest source of fine opal.  Metaphysical practitioners believe that opal enhances love between faithful lovers, but because it intensifies all thoughts and actions, including those that are negative, it must be worn judiciously.  Opal is the birthstone for the month of October and the national gemstone of Australia.

COLLECTORS’ INFORMATION: Opal specimens are collected for their rarity and especially for their fiery play of opalescent colors.