opal, Mexico, gems

Gübelin describes the opal deposits of Mexico, concentrating on the important occurrences in Querétaro and their characteristic transparent to translucent precious and fire opals. He discusses the volcanic geological setting, occurrence of opal in cavities and fractures in rhyolitic rocks, mining and recovery of the material, and the considerable range of body colors and play-of-color displayed by Mexican opals. Particular attention is given to the internal characteristics of the stones, including mineral and fluid inclusions, and to the differences between Mexican volcanic opal and opal from other major producing regions. The article provides both a description of the deposits and a gemological characterization of their products. Gübelin’s article is subsequently cited specifically for opal from the Carbonera mine at La Trinidad, Querétaro.