gemstone
Boulder Opal
Hydrated amorphous silica (SiO2·nH2O) with ironstone matrix
AI-generated identification · may be incorrectHardness of 5.5-6.5 on the Mohs scale, vitreous to waxy luster, amorphous crystal structure, and exhibits a vibrant play-of-color against a brown ironstone host.
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Physical properties
Hardness of 5.5-6.5 on the Mohs scale, vitreous to waxy luster, amorphous crystal structure, and exhibits a vibrant play-of-color against a brown ironstone host.
Formation & geological history
Formed in shallow, seasonally dry inland basins where silica-rich groundwater filled cracks and voids in ironstone rock formations.
Uses & applications
Primarily used in high-end jewelry, including rings, pendants, and collector display cabochons.
Geological facts
Boulder opal is uniquely mined in the state of Queensland, Australia, where the opal is intricately connected to its host ironstone matrix.
Field identification & locations
Easily identified by patches of brilliant spectral colors flashing from within natural brown ironstone host rock. Common in the Quaternary and Cretaceous deposits of Australia.
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