mineral

Brown chalcedony (likely carnelian or agate fragment)

Microcrystalline quartz, SiO₂; iron-oxide-colored chalcedony

AI-generated identification · may be incorrect

Typically hardness 6.5–7 Mohs, waxy to dull luster, translucent brown-orange color, and conchoidal fracture; crystals are microscopic and cleavage is absent. The specimen appears rough and naturally broken, with possible lighter chalcedony or host material along its edge.

Identified September 15, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities, fractures, or vesicles in volcanic rocks, later colored by dispersed iron oxides. Chalcedony deposits range from Precambrian to recent, depending on the host rock and locality.

Uses & applications

Used for beads, cabochons, carvings, ornaments, and lapidary material; attractive translucent pieces may have modest gemstone value.

Geological facts

Carnelian is orange-red chalcedony, while brown varieties are often called sard or brown chalcedony; boundaries between these trade names are subjective.

Field identification & locations

Common in volcanic terrains, sedimentary silica deposits, and gravel beds worldwide, including Brazil, Uruguay, India, Madagascar, and the western United States. Test by its glassy conchoidal fracture and hardness, but avoid scratching it if polished or valuable.