sedimentary

Greywacke

Lithic Sandstone (Greywacke)

Hardness: 6-7 Mohs; Color: Dull grey, greenish-grey, or black; Luster: Dull/Earthy; Crystal structure: Clastic (angular grains in fine matrix); Specific Gravity: 2.6-2.7

Hardness: 6-7 Mohs
Color: Dull grey, greenish-grey, or black
Luster: Dull/Earthy

Identified July 2, 2026More sedimentary →

Explore Greywacke in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6-7 Mohs; Color: Dull grey, greenish-grey, or black; Luster: Dull/Earthy; Crystal structure: Clastic (angular grains in fine matrix); Specific Gravity: 2.6-2.7

Formation & geological history

Formed from the rapid deposition of poorly sorted sediment in deep-marine environments, often via turbidity currents. They are common in orogenic belts and range from Paleozoic to more recent ages.

Uses & applications

Used primarily as crushed stone for road construction, railroad ballast, and high-quality concrete aggregate due to its hardness and durability.

Geological facts

Often called 'dirty sandstone' because of its poorly sorted nature and high clay content. It is a key indicator of ancient deep-sea trench environments and tectonic activity.

Field identification & locations

Identify by its characteristic 'salt and pepper' appearance of dark and light grains, extreme hardness compared to other sandstones, and lack of visible bedding in small hand samples.