gemstone

Tumbled carnelian (reddish-brown chalcedony)

Microcrystalline quartz, SiO₂; chalcedony variety, likely iron-stained carnelian

AI-generated identification · may be incorrect

Mohs hardness 6.5–7; reddish-brown, translucent to opaque, and vitreous to waxy luster with no visible cleavage. It has a cryptocrystalline quartz structure and typically specific gravity around 2.60–2.65.

Identified September 3, 2026More gemstone →

Explore Tumbled carnelian (reddish-brown chalcedony) in the encyclopedia →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities or fractures, later acquiring red-brown color from finely dispersed iron oxides. Most examples are Cenozoic to older volcanic-associated deposits, though exact age cannot be determined from the image.

Uses & applications

Used for beads, cabochons, carvings, seals, and ornamental objects; durable tumbled pieces are popular inexpensive gemstones.

Geological facts

Carnelian is a long-used gemstone found in ancient Egyptian, Greek, Roman, and Islamic jewelry. Heating can intensify or alter its red-orange color.

Field identification & locations

Identify it by uniform warm red-brown color, translucency at thin edges, waxy polish, and lack of banding or cleavage; it will scratch glass but not be scratched by a steel knife. Common sources include India, Brazil, Uruguay, Madagascar, and the United States.