mineral

Chalcedony (likely common gray chalcedony)

Microcrystalline quartz, SiO₂

AI-generated identification · may be incorrect

Usually hardness 6.5–7, waxy to dull luster, translucent to opaque gray-blue color, and no visible cleavage; it commonly breaks with smooth to conchoidal fracture. The rounded, cloudy appearance suggests naturally worn chalcedony rather than a crystalline quartz specimen.

Identified August 12, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities, fractures, or vesicles in volcanic and sedimentary rocks, precipitating as microscopic quartz fibers. Deposits range from ancient to modern, and the specimen may have been transported and rounded in gravel or along a beach.

Uses & applications

Used for lapidary carvings, cabochons, beads, ornaments, and decorative stone; massive gray material has modest commercial value.

Geological facts

Chalcedony is a quartz variety encompassing several color varieties, including agate, carnelian, chrysoprase, and onyx. Its fine-grained structure makes it tougher and less sparkly than ordinary quartz crystals.

Field identification & locations

Identify it by its waxy surface, uniform cryptocrystalline texture, lack of cleavage, and ability to scratch glass. Common sources include volcanic terrains, river gravels, and coastal beaches worldwide; acid testing is unnecessary and may damage the specimen.