mineral

Botryoidal chalcedony (likely blue-gray agate)

Chalcedony, microcrystalline quartz (SiO₂), commonly with iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; translucent blue-gray to cream with rusty brown patches, waxy-to-dull luster, and no obvious cleavage. It has a cryptocrystalline quartz structure and conchoidal fracture; the rounded surface growths suggest botryoidal texture.

Identified September 5, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, precipitating layers of chalcedony; iron oxides create the brown coloration. The exact geological age and locality cannot be determined from the image.

Uses & applications

Used as a lapidary and ornamental material, including cabochons, carvings, and display specimens; attractive translucent pieces may be sold as agate or chalcedony.

Geological facts

The specimen may also be described commercially as “blue chalcedony,” “plume agate,” or “botryoidal agate,” though appearance alone cannot establish a precise variety.

Field identification & locations

Look for translucent edges, a waxy luster, conchoidal fracture, and hardness sufficient to scratch ordinary glass; it should not fizz in dilute hydrochloric acid. Common sources include volcanic terrains in Brazil, Mexico, Uruguay, Namibia, and the western United States.