sedimentary

Graywacke

Lithic Sandstone (Graywacke)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs scale); Color: Gray to dark greenish-gray; Luster: Dull to earthy; Crystal structure: Clastic (poorly sorted mineral grains such as quartz, feldspars, and rock fragments in a clay matrix); Cleavage: None; Specific gravity: 2.6-2.7

Hardness: 6-7 (Mohs scale)
Color: Gray to dark greenish-gray
Luster: Dull to earthy

Identified June 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by rapid deposition of sediments in deep marine environments via turbidity currents (underwater landslides). Typical of geosynclinal accumulation, often dating back to the Paleozoic or Precambrian eras.

Uses & applications

Primarily used in construction as crushed stone for road base, concrete aggregate, and railway ballast. Due to its durability, it is also used for paving stones.

Geological facts

Graywacke is often called 'dirty sandstone' because of its poorly sorted nature and high clay content. It is a key indicator of ancient active tectonic plate margins.

Field identification & locations

Identify in the field by its dark, gritty appearance, extreme hardness compared to other sandstones, and the presence of angular rock fragments. It is commonly found in mountainous regions or ancient folded mountain belts.