gemstone
Polished opal-bearing rock (likely boulder opal)
Opal, hydrated amorphous silica (SiO₂·nH₂O), in ironstone or host rock
AI-generated identification · may be incorrectThe specimen has a blue-lavender polished face with pale host-rock patches. Opal has no crystal structure or cleavage, Mohs hardness about 5.5–6.5, and a vitreous to waxy luster; the photo alone does not confirm play-of-color.
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Physical properties
The specimen has a blue-lavender polished face with pale host-rock patches. Opal has no crystal structure or cleavage, Mohs hardness about 5.5–6.5, and a vitreous to waxy luster; the photo alone does not confirm play-of-color.
Formation & geological history
Silica-rich water deposited hydrated silica in fractures or cavities in host rock; opal commonly forms in sedimentary environments, often in Cretaceous-age Australian deposits.
Uses & applications
Used for cabochons, jewelry, and collecting; the host rock may be retained as part of the natural specimen.
Geological facts
Boulder opal is cut with its ironstone host attached, which can support thin opal seams.
Field identification & locations
Look for a distinct opal seam or shifting spectral flashes when the stone is tilted; common sources include Queensland, Australia. This image does not establish locality or whether the blue is natural or treated.
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