sedimentary

Greywacke (River Pebble)

Dirty Sandstone (SiO2 with lithic fragments)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Grey to dark greenish-grey; Luster: Dull to earthy; Crystal Structure: Clastic matrix-supported; Cleavage: None; Specific Gravity: 2.6-2.7

Hardness: 6-7 on Mohs scale
Color: Grey to dark greenish-grey
Luster: Dull to earthy

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Grey to dark greenish-grey; Luster: Dull to earthy; Crystal Structure: Clastic matrix-supported; Cleavage: None; Specific Gravity: 2.6-2.7

Formation & geological history

Formed by the rapid deposition of poorly sorted sediment in deep ocean basins via turbidity currents (underwater landslides). Usually Paleozoic to Mesozoic in age.

Uses & applications

Primarily used in construction as road base, aggregate, and railroad ballast. Smooth river-worn specimens are popular for rock painting and decorative landscaping.

Geological facts

Greywacke is often called 'dirty sandstone' because it contains a large amount of fine-grained clay matrix and diverse rock fragments, unlike pure quartz sandstone.

Field identification & locations

Identify by its 'salt and pepper' look under a lens, its extreme hardness compared to slate, and its lack of visible layering. Found commonly in mountainous regions and riverbeds.