mineral

Gray chalcedony (microcrystalline quartz)

Chalcedony, SiO₂; likely common gray/blue-gray variety

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray to bluish-gray, waxy to dull luster, cryptocrystalline structure, conchoidal fracture, no cleavage, specific gravity about 2.6. The rough, rounded piece appears naturally weathered or fractured.

Identified August 10, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, precipitating as microscopic quartz fibers. It commonly formed during the Cenozoic or older, depending on its host rock and locality.

Uses & applications

Used for cabochons, carvings, beads, and ornamental stone; massive common material has modest lapidary value.

Geological facts

Chalcedony is a broad quartz variety that includes translucent gray, blue, white, and brown material; banded forms may be classified as agate.

Field identification & locations

Identify with its waxy appearance, translucency, conchoidal fracture, and resistance to scratching by a steel knife; it should not fizz in dilute acid. Common in volcanic terrains worldwide, including Brazil, India, Mexico, Turkey, and the western United States.