mineral

Brown chalcedony (likely carnelian/agate)

Cryptocrystalline quartz, SiO₂; iron-bearing chalcedony

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent brown to amber with milky zones, vitreous-to-waxy luster, and no visible cleavage. It has a microcrystalline quartz structure and typically conchoidal fracture; specific gravity is about 2.6.

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, with iron oxides producing the brown coloration. Individual pieces may range from relatively young weathering deposits to Paleozoic or Mesozoic volcanic-hosted material.

Uses & applications

Used as a lapidary stone, cabochon, bead, carving material, and ornamental specimen; attractive transparent sections may be sold as agate or carnelian.

Geological facts

The image shows a rough, partly translucent silica nodule with brown iron staining, but exact identification cannot be certain without testing or a locality label.

Field identification & locations

Common in volcanic terrains and alluvial gravels worldwide, including Brazil, Uruguay, India, Madagascar, Mexico, and the western United States. Field tests include conchoidal fracture, lack of cleavage, glassy/waxy surfaces, and scratching glass; acid does not fizz.