sedimentary

Banded Greywacke

Greywacke (Lithic wacke)

Hardness: 6-7 on Mohs scale; Color: Dark grey with white quartz/calcite veins; Luster: Dull to earthy; Texture: Fine to medium-grained; Structure: Bedded with cross-cutting veins.

Hardness: 6-7 on Mohs scale
Color: Dark grey with white quartz/calcite veins
Luster: Dull to earthy

Identified July 4, 2026More sedimentary →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Dark grey with white quartz/calcite veins; Luster: Dull to earthy; Texture: Fine to medium-grained; Structure: Bedded with cross-cutting veins.

Formation & geological history

Formed from the rapid deposition of muddy sandstone in deep marine environments (turbidity currents). The white veins formed later when tectonic stress caused fractures that were filled by mineral-rich hydrothermal fluids.

Uses & applications

Primarily used as high-quality aggregate for road construction, concrete, and railway ballast due to its extreme hardness and durability.

Geological facts

Greywacke is often called 'dirty sandstone' because it contains a large amount of clay and diverse rock fragments. It is a signature rock of ancient mountain-building events (orogenies).

Field identification & locations

Identify in the field by its dark color, toughness, and the presence of thin mineral veins. Commonly found in riverbeds and coastal regions near old mountain ranges. Great for skipping stones.