sedimentary

Weathered fine-grained rock, likely mudstone or siltstone

Indeterminate clastic sedimentary rock; likely lithified clay- and silt-sized grains

AI-generated identification · may be incorrect

Dull, brown-gray, fine-grained, with blocky fracture and a weathered, lighter surface. Typical mudstone/siltstone hardness is about 2–4 Mohs; the image does not show diagnostic crystals or cleavage.

Identified October 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed from compacted and cemented mud or silt in a quiet-water setting, then exposed and weathered. Its age and exact origin cannot be determined from the photograph.

Uses & applications

Commonly used as aggregate or fill when suitable, and useful as a geological teaching or collection specimen; this piece has no obvious gem or ornamental value.

Geological facts

Mudstone and siltstone are distinguished chiefly by grain size, which usually requires close inspection or magnification.

Field identification & locations

The fine, dull texture and blocky shape suggest a sedimentary rock, but a fresh broken surface and hand lens would help distinguish it from weathered volcanic rock. Such rocks occur widely in sedimentary basins worldwide.