Gem-name guide / Gem variety

Boulder Opal

SiO₂·nH₂O

Boulder Opal is indexed as a gem variety in this gem-name directory. The CIBJO nomenclature table associates this name with Opal. Gem names may describe appearance or a material family; a name alone does not identify treatments, origin or quality.

Material or mineral family: Opal
Name classification: Gem variety

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Names describe materials, not the authenticity, treatment, provenance or quality of a particular specimen. Physical properties vary for mixed materials; values absent from this guide have not been estimated.

Reference snapshot: September 2026. Source dates and uncertainties are retained in the record.