mineral

Rough chalcedony (likely agate/quartz vein)

Chalcedony, microcrystalline SiO₂; possibly agate with iron-oxide-stained host rock

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; translucent blue-gray to cream material with waxy-to-glassy luster, white quartz-like fracture, and brown iron-oxide matrix. Chalcedony is cryptocrystalline quartz and lacks visible cleavage.

Identified August 21, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rock, commonly during the Cenozoic or older volcanic episodes; iron oxides create the brown staining. Exact age and locality cannot be determined from the image.

Uses & applications

Used for cabochons, carvings, beads, lapidary pieces, and ornamental stone; tougher, attractive varieties are used in jewelry and small decorative objects.

Geological facts

The blue-gray translucent portion may be chalcedony, while the surrounding brown material could be weathered volcanic rock or iron-stained quartz. A polished surface would better reveal any agate banding.

Field identification & locations

Look for waxy translucency, conchoidal fracture, and hardness sufficient to scratch glass; it should not be confused with ordinary glass or calcite. Common worldwide, especially in volcanic regions such as Brazil, Uruguay, Mexico, India, and the western United States.