mineral
Polished common opal
Opal, hydrated amorphous silica (SiO₂·nH₂O)
AI-generated identification · may be incorrectCreamy white with pale green and peach patches and a polished luster; the visible crack-like lines may be matrix or fractures. Hardness is about 5.5–6.5 Mohs; amorphous, with no cleavage. The image does not show enough detail to confirm play-of-color.
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Physical properties
Creamy white with pale green and peach patches and a polished luster; the visible crack-like lines may be matrix or fractures. Hardness is about 5.5–6.5 Mohs; amorphous, with no cleavage. The image does not show enough detail to confirm play-of-color.
Formation & geological history
Silica-rich water deposited gel in rock cavities or fractures, later hardening into opal; it forms in varied settings and ages, commonly in volcanic rocks and weathered sediments.
Uses & applications
Used for cabochons, beads, and ornamental objects; common opal is also collected as a decorative stone.
Geological facts
Unlike crystalline quartz, opal lacks a long-range crystal structure and may contain several percent water.
Field identification & locations
Check for natural-looking color zoning and a smooth, waxy polish; confirm identity with gemological tests, since appearance alone cannot distinguish opal from other pale stones. Opal occurs notably in Australia, Ethiopia, Mexico, and the western United States.
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