sedimentary

River Pebble (Greywacke / Basalt Pebble)

Indeterminate Rounded Pebble (composed of quartz, feldspar, or mafic minerals)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale. Color: Dull greenish-grey to dark charcoal grey. Luster: Earthy to dull. Cleavage: None (massive, fine-grained texture). Specific Gravity: Approximately 2.6 - 2.9.

Hardness: 6-7 on Mohs scale
Color: Dull greenish-grey to dark charcoal grey
Luster: Earthy to dull

Identified July 27, 2026More sedimentary →

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Physical properties

Hardness: 6-7 on Mohs scale. Color: Dull greenish-grey to dark charcoal grey. Luster: Earthy to dull. Cleavage: None (massive, fine-grained texture). Specific Gravity: Approximately 2.6 - 2.9.

Formation & geological history

Formed through the erosion, transport, and rounding of fine-grained igneous or sedimentary rocks by river currents, glacial melt, or wave action over thousands to millions of years.

Uses & applications

Primarily used as river rock landscaping material, construction aggregate, concrete filler, and decorative aquascaping stones.

Geological facts

Water-worn river pebbles get their smooth, rounded shape through natural mechanical abrasion over long distances in rivers or ocean shores.

Field identification & locations

Commonly found in stream beds, river channels, glacial till, and coastal beaches worldwide. Identified by its smooth rounded surface, dull earthy tone, and hard fine-grained matrix.