sedimentary

Graywacke (Sandstone)

Lithic Sandstone (Graywacke)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs); Color: Dark gray to greenish-gray; Luster: Dull; Texture: Fine to medium-grained, poorly sorted, angular grains; Structure: Competent, often heavily fractured or folded.

Hardness: 6-7 (Mohs)
Color: Dark gray to greenish-gray
Luster: Dull

Identified July 20, 2026More sedimentary →

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Physical properties

Hardness: 6-7 (Mohs); Color: Dark gray to greenish-gray; Luster: Dull; Texture: Fine to medium-grained, poorly sorted, angular grains; Structure: Competent, often heavily fractured or folded.

Formation & geological history

Formed in high-energy marine environments through turbidity currents (turbidites) that deposit sediment rapidly in deep-ocean trenches. Common in accretionary prisms along convergent plate boundaries.

Uses & applications

Primarily used as aggregate in road construction, railroad ballast, and high-strength concrete because of its extreme hardness and resistance to weathering.

Geological facts

Graywacke is often called the 'dirty sandstone' because of its high clay matrix content. It is a major component of the Franciscan Complex in California.

Field identification & locations

Identify by its characteristic 'slatey' gray color, extreme toughness, and common occurrence in coastal cliffs showing intense folding or quartz veining.