sedimentary

Greywacke (Sandstone)

Lithic wacke

Hardness: 6-7 Mohs; Color: Dull grey to greenish-grey; Luster: Earthy to dull; Structure: Poorly sorted clastic texture with a fine-grained clay matrix; Specific Gravity: 2.6-2.7

Hardness: 6-7 Mohs
Color: Dull grey to greenish-grey
Luster: Earthy to dull

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 6-7 Mohs; Color: Dull grey to greenish-grey; Luster: Earthy to dull; Structure: Poorly sorted clastic texture with a fine-grained clay matrix; Specific Gravity: 2.6-2.7

Formation & geological history

Formed through rapid deposition in deep marine environments (turbidity currents) where minerals and rock fragments don't have time to sort by size. Typically Paleozoic or Mesozoic in age.

Uses & applications

Used primarily in road construction as sub-base material, as concrete aggregate, and occasionally for flagstones or decorative landscaping.

Geological facts

Greywacke is often called a 'dirty sandstone' because of its poorly sorted nature and high clay content. It is a common indicator of ancient submarine landslides called turbidites.

Field identification & locations

Identify by its dark color, hardness, and visible but poorly sorted grains. Commonly found in mountainous regions near former tectonic subduction zones or along rocky riverbeds and coastlines.