sedimentary

Tumbled sandstone pebble

Quartz-rich sandstone, likely ferruginous or calcareous sandstone

AI-generated identification · may be incorrect

Tan-brown, fine-grained, rounded and polished; dull to slightly silky luster with visible pores and tiny dark iron-oxide grains. Hardness is approximately 6–7 for quartz grains, but the cement may be softer; no obvious cleavage and generally low-to-moderate specific gravity (~2.2–2.6).

Identified September 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Sandstone formed when quartz-rich sand was deposited, compacted, and cemented by silica, calcite, or iron oxides, commonly in ancient rivers, beaches, dunes, or shallow seas. Its exact geological age cannot be determined from the image.

Uses & applications

Used as a building and paving stone, aggregate, and ornamental material; polished pebbles are mainly decorative or collectible and have little gem value.

Geological facts

The rounded outline and smooth surface indicate natural water abrasion or deliberate tumbling. Small pores and scattered reddish grains are consistent with cemented sand and iron staining.

Field identification & locations

Identify it by its sandy texture, tiny quartz grains, porous appearance, and lack of large interlocking crystals; a glass-scratch test may show quartz-rich grains scratching glass. Common worldwide, especially in sedimentary basins and riverbeds.