Resinite opal from Saint-Pierre-Eynac, Saint-Julien-Chapteuil, Haute-Loire, Auvergne-Rhône-Alpes, France. Comes with certificate of authenticity. Average weight (Carats): 704.9 carats. Dimensions (mm): 83 x 77 x 30 mm. Ref. : SKU031867. Mineraloid composed of hydrated silica, of formula SiO2·nH2O, with traces of aluminum, potassium, sodium and calcium, opal sometimes contains crystallites of cristobalite, sometimes showing tridymite-type stacking faults. The term opal comes from the Sanskrit word upala meaning “precious stone”.