mineral

Translucent chalcedony (likely agate or common opal)

Microcrystalline quartz, SiO₂; possible hydrated silica opal, SiO₂·nH₂O

AI-generated identification · may be incorrect

Pale honey-yellow to gray, translucent, waxy to dull luster, with curved/conchoidal fracture and irregular fibrous or botryoidal banding. Chalcedony hardness is about 6.5–7 Mohs; opal is softer, about 5.5–6.5.

Identified August 8, 2026More mineral →

Explore Translucent chalcedony (likely agate or common opal) in the encyclopedia →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rock, precipitating in layers over time; ages may range from recent to hundreds of millions of years. The image may show a naturally weathered or cut fragment illuminated from behind.

Uses & applications

Used for cabochons, carvings, beads, decorative objects, and collectible specimens; translucent agate and opal varieties are also used in jewelry.

Geological facts

Yellow coloration commonly comes from iron staining or inclusions. Strong internal glow and cloudy, curved bands are typical of chalcedony or common opal rather than crystalline quartz.

Field identification & locations

Test hardness carefully on an inconspicuous edge, inspect for concentric banding, and check whether it scratches glass; opal generally will not, while chalcedony usually will. Common sources include volcanic regions of Brazil, Uruguay, Mexico, the western United States, and Australia.