mineral

Chalcedony (likely agate/chert fragment)

Microcrystalline quartz, SiO₂

AI-generated identification · may be incorrect

Hardness 6.5–7; pale gray-green to cream, translucent edges, waxy to dull luster, and no visible cleavage. The irregular fracture and fine-grained texture are characteristic of chalcedony, though the image alone cannot confirm a specific variety.

Identified August 11, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities, fractures, or vesicles in volcanic rocks and later crystallizes as microcrystalline quartz. It commonly formed in the Cenozoic and older volcanic terrains, with age depending on its host rock.

Uses & applications

Used for carvings, cabochons, beads, abrasives, and decorative stone; attractive banded varieties are sold as agate. This small rough fragment has modest commercial value.

Geological facts

Chalcedony is quartz composed of microscopic intergrowths of quartz varieties such as moganite and quartz. Color may result from iron, manganese, clay, or other impurities.

Field identification & locations

Identify by its waxy appearance, translucent margins, conchoidal fracture, and hardness sufficient to scratch ordinary glass; acid produces no reaction. Common sources include Brazil, Uruguay, India, Madagascar, Turkey, and many volcanic regions worldwide.