gemstone

Tumbled carnelian agate (probable)

Cryptocrystalline quartz, SiO₂; chalcedony variety colored by iron oxides

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; orange-brown, translucent to opaque, waxy-to-vitreous luster, with no visible cleavage and conchoidal fracture. The rounded, polished shape indicates tumbling; faint banding or cloudy chalcedony texture is visible.

Identified August 10, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, later incorporating iron oxides that produce orange-red color. It may range from Cenozoic to much older, depending on its host rock and locality.

Uses & applications

Used for cabochons, beads, carvings, ornamental objects, and inexpensive jewelry; tumbled pieces are common collectors’ specimens.

Geological facts

Carnelian is an orange-red chalcedony, while “sard” generally refers to darker brown-red material; commercial labels often overlap. Heating can intensify its color.

Field identification & locations

Identify by its orange translucency, hardness, waxy luster, and lack of cleavage; glass may look similar but is often more uniformly clear and bubbles may occur. Common sources include India, Brazil, Uruguay, Madagascar, and the United States.