sedimentary

Siltstone River Rock

Siltstone (composed of silt-sized particles, silicate minerals)

AI-generated identification · may be incorrect

Hardness: 3-6 Mohs; Color: Brown, tan, earthy tones; Luster: Dull or earthy; Structure: Clastic, fine-grained; Cleavage: Generally poor, can be fissile if clay content is high.

Hardness: 3-6 Mohs
Color: Brown, tan, earthy tones
Luster: Dull or earthy

Identified July 6, 2026More sedimentary →

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Physical properties

Hardness: 3-6 Mohs; Color: Brown, tan, earthy tones; Luster: Dull or earthy; Structure: Clastic, fine-grained; Cleavage: Generally poor, can be fissile if clay content is high.

Formation & geological history

Formed through the accumulation and cementation of silt particles in low-energy aquatic environments like river deltas, floodplains, or lakes. This specimen shows significant rounding due to fluvial (river) erosion over many years.

Uses & applications

Used primarily as low-grade construction fill, garden landscaping, or decorative river stones. Occasionally used in cement production.

Geological facts

Siltstone is the bridge between sandstone (coarser) and shale (finer). Large, elongated river stones like this were historically used as primitive grinding stones or anchors.

Field identification & locations

Identify by its gritty texture (finer than sandpaper but rougher than shale) and lack of visible crystalline structure. Found in riverbeds and ancient sedimentary basins worldwide.