sedimentary

River Pebble (Greywacke or Quartzite-rich Sandstone)

Lithic Sandstone (primarily SiO2 with rock fragments)

Hardness: 6-7 Mohs; Color: Dull grey to brownish-grey; Luster: Matte/Earthy; Structure: Fine-grained clastic; Specific Gravity: approx. 2.6-2.7. Shows a smooth, water-worn texture with small white quartz veinlets.

Hardness: 6-7 Mohs
Color: Dull grey to brownish-grey
Luster: Matte/Earthy

Identified March 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of sand and rock fragments in marine or fluvial environments, followed by lithification. This specific specimen has been further shaped by high-energy water transport (river or beach erosion) over thousands of years.

Uses & applications

Commonly used in construction aggregate, landscaping (river rocks), and as decorative filler for gardens and pathways. Geologically, they are used to study ancient water flow patterns.

Geological facts

River stones like this are often rounded into 'prolate' or 'oblate' spheroids due to a process called saltation, where stones bounce along a riverbed, chipping away sharp edges.

Field identification & locations

Identify in the field by its smooth, elliptical shape and lack of visible large crystals. It is non-reactive to acid unlike limestone. Common everywhere in glacial tills, stream beds, and coastlines.

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