sedimentary

Gray Pebble (Graywacke / Basalt)

Graywacke (or fine-grained Basalt)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Dull medium to dark gray with subtle speckling; Luster: Matte, earthy; Texture: Fine-grained, stream-rounded; Cleavage: None

Hardness: 6-7 on Mohs scale
Color: Dull medium to dark gray with subtle speckling
Luster: Matte, earthy

Identified July 22, 2026More sedimentary →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Dull medium to dark gray with subtle speckling; Luster: Matte, earthy; Texture: Fine-grained, stream-rounded; Cleavage: None

Formation & geological history

Formed through sedimentary deposition of poorly sorted sand grains in underwater environments, or through cooling of mafic lava, subsequently rounded by stream or wave erosion.

Uses & applications

Commonly used as construction aggregate, landscaping gravel, or river rock for decorative gardens.

Geological facts

Water-worn rounded pebbles often travel dozens to hundreds of miles down river systems, undergoing mechanical weathering that polishes their edges into smooth, sub-angular to rounded shapes.

Field identification & locations

Identified by its uniform gray color, fine texture, and smooth, rounded water-worn shape. Found along riverbeds, beaches, and glacial gravel deposits worldwide.