mineral

Polished agate or chalcedony pebble

Microcrystalline quartz (SiO₂), likely chalcedony/agate

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray-brown color with a waxy to glassy luster and a pale internal fracture or band. Quartz has a trigonal crystal structure, but microscopic fibers make chalcedony appear noncrystalline; no obvious cleavage, conchoidal fracture, specific gravity about 2.6.

Identified September 22, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited successive layers in cavities and fractures, commonly in volcanic rocks; age varies widely, from Paleozoic to Cenozoic. The rounded form is natural abrasion, with polishing likely enhancing the surface.

Uses & applications

Used for lapidary cabochons, beads, carvings, and ornamental objects; common polished specimens have modest collecting value.

Geological facts

Agate is a banded variety of chalcedony, while uniformly colored material is usually called chalcedony. Its curved, shell-like fracture and hardness distinguish it from glass and many softer stones.

Field identification & locations

Common in volcanic terrains worldwide, especially Brazil, Uruguay, Mexico, India, and the western United States. Look for waxy translucency, conchoidal fracture, resistance to scratching by steel, and possible curved or fine banding.