mineral

Gray chalcedony (microcrystalline quartz)

Chalcedony, SiO₂; a cryptocrystalline variety of quartz

AI-generated identification · may be incorrect

Translucent gray-white with a waxy to vitreous luster and irregular, conchoidal-looking fracture; Mohs hardness about 6.5–7. Individual crystals are microscopic, so crystal form is not visible; the rough specimen’s density and exact identity cannot be established from the image alone.

Identified October 10, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich fluids deposit very fine quartz in cavities and fractures, commonly in volcanic rocks. Chalcedony occurs in rocks of many ages; the specimen’s age and locality cannot be determined visually.

Uses & applications

Used for carvings, beads, cabochons, and ornamental objects; common rough pieces are also collected.

Geological facts

Chalcedony includes agate, carnelian, and onyx varieties, distinguished partly by color and banding.

Field identification & locations

The cloudy translucence, waxy sheen, and hardness help distinguish it from softer glassy materials; it occurs worldwide, often in volcanic cavities and veins. A scratch test on an inconspicuous area and locality information would improve identification.