sedimentary

Graywacke

Lithic Sandstone (Graywacke)

Hardness: 6-7 on Mohs scale; Color: Dark gray to greenish-gray; Luster: Dull/Earthy; Structure: Fine-to-medium grained matrix with angular fragments; Cleavage: None (conchoidal fracture).

Hardness: 6-7 on Mohs scale
Color: Dark gray to greenish-gray
Luster: Dull/Earthy

Identified June 16, 2026More sedimentary →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Dark gray to greenish-gray; Luster: Dull/Earthy; Structure: Fine-to-medium grained matrix with angular fragments; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed in deep-sea environments through turbidity currents (underwater landslides) that deposit poorly sorted sediment. Typically found in paleozoic or mesozoic deep-marine basins.

Uses & applications

Primarily used as construction aggregate, road base, and railroad ballast due to its hardness and durability.

Geological facts

Graywacke is often called 'dirty sandstone' because it contains a large amount of clay and silt along with sand-sized quartz and feldspar grains.

Field identification & locations

Identify by its characteristic 'salt and pepper' look under a lens, its extreme hardness, and lack of distinct bedding layers compared to other sandstones. Ubiquitous in orogenic belts.