mineral

Tumbled chalcedony or agate fragment

Microcrystalline quartz (SiO₂), likely chalcedony; exact identification is limited by the small, opaque image

AI-generated identification · may be incorrect

Typically hardness 6.5–7 Mohs, waxy to vitreous luster, gray-brown to reddish color, and no visible cleavage; cryptocrystalline structure with conchoidal fracture. The rounded form suggests natural abrasion or tumbling.

Identified August 15, 2026More mineral →

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Physical properties

Formation & geological history

Chalcedony forms when silica-rich groundwater fills cavities and fractures, often in volcanic rocks; agate is banded chalcedony. Deposits range from ancient to recent, commonly associated with basalt and weathered gravels.

Uses & applications

Used for carvings, cabochons, beads, knife edges, abrasives, and decorative stone. Small common pieces have modest collector value.

Geological facts

Chalcedony can be translucent at thin edges and may show subtle banding, mossy inclusions, or color zoning. Iron and other impurities produce brown, red, orange, or gray tones.

Field identification & locations

Test hardness against glass, inspect for waxy luster and conchoidal fracture, and check for banding with a strong light; it should not scratch easily with a steel knife. Common in volcanic regions, river gravels, and agate-bearing areas.