sedimentary

River Stone (likely Mudstone or Siltstone)

Lutite (Clastic sedimentary rock composed of clay and silt-sized particles)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs scale); Color: Gray to olive-brown; Luster: Dull/Matte; Structure: Microcrystalline with no visible grains; Cleavage: None (conchoidal fracture possible); Specific Gravity: 2.4-2.8.

Hardness: 3-4 (Mohs scale)
Color: Gray to olive-brown
Luster: Dull/Matte

Identified March 23, 2026More sedimentary →

Explore River Stone (likely Mudstone or Siltstone) in the encyclopedia →

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Physical properties

Formation & geological history

Formed through the lithification of suspended particles (mud and clay) in low-energy aquatic environments like lake beds or deep ocean floors. This specimen's rounded shape indicates it was later eroded and smoothed by high-energy water transport, such as in a river or stream.

Uses & applications

Used primarily in landscaping, decorative rock gardens, and construction aggregate. Extremely smooth specimens are often used for stone painting, 'worry stones,' or in hot stone massage therapy.

Geological facts

Rocks like these are the most common source of well-preserved fossils, as the fine sediment can trap organic matter without damaging it. This specific specimen has undergone 'abrasion,' a mechanical weathering process that acts like a natural rock tumbler.

Field identification & locations

Identify in the field by its smooth, egg-like texture and lack of visible mineral grains. It will not scratch glass but often feels slightly 'soapy' or silken when wet. Found globally in riverbeds, beaches, and glacial till.