sedimentary

Rounded quartz-rich pebble

Likely chert or quartzite; predominantly microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; pale tan-gray, dull to slightly waxy luster, fine-grained and massive, with no visible cleavage. Its smooth, rounded shape indicates water abrasion; minor iron staining or weathered inclusions may produce the yellow-brown patches.

Identified September 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Probably formed as a silica-rich sedimentary nodule (chert) or metamorphosed quartz sandstone (quartzite), then eroded and transported in a stream or beach environment. The specimen’s exact geological age and local source cannot be determined from the photograph.

Uses & applications

Common material for landscaping, tumbling, lapidary work, and occasional toolmaking; attractive pieces may be used as decorative stones, but this example has little commercial value.

Geological facts

Quartz-rich rocks resist weathering, so they commonly survive transport as smooth pebbles. A steel file or glass-scratch test can help distinguish it from softer limestone, though testing may mark the specimen.

Field identification & locations

Look for a very hard, nonporous pebble that scratches glass and shows little or no reaction to dilute hydrochloric acid; quartzite is typically granular, while chert is more uniformly waxy and may show conchoidal fracture. Common in river gravels, beaches, and glacial deposits.