sedimentary

Rounded graywacke or sandstone cobble

Lithified clastic sandstone; likely quartz–feldspar–lithic grain aggregate in a silica or calcite matrix

AI-generated identification · may be incorrect

Gray-brown, rounded, fine- to medium-grained cobble with darker streaks and weathered pitting; typically Mohs 6–7, dull to slightly gritty luster, no obvious cleavage, and specific gravity about 2.3–2.7. The exact mineralogy cannot be confirmed from the photograph alone.

Identified August 19, 2026More sedimentary →

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At a glance

Common name: Rounded graywacke or sandstone cobble
Scientific name: Lithified clastic sandstone; likely quartz–feldspar–lithic grain aggregate in a silica or calcite matrix
Category: sedimentary
Identified: August 19, 2026
Method: Standard

AI Estimated Value

$0–$5 as an ordinary found cobble; roughly $5–$20 if unusually attractive, polished, or sold as a display specimen.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Formed when sand-sized sediment was deposited, compacted, and cemented, then rounded by transport in a river, beach, or glacial environment. Its precise geological age and source cannot be determined visually.

Uses & applications

Commonly used as landscaping stone, aggregate, paving material, and road base; attractive pieces may be collected, but this specimen has little commercial gemstone value.

Geological facts

The dark bands may represent lithic fragments, iron staining, bedding, or weathering rather than true foliation. The surrounding dark pavement is man-made asphalt, but the central cobble is a natural geological specimen.

Field identification & locations

Look for visible sand grains, irregular bedding or streaks, gritty texture, and lack of vesicles or large interlocking crystals; a streak, acid, hardness, and thin-section tests would refine identification. Sandstones occur worldwide, especially in sedimentary basins and river gravels.