sedimentary

Graywacke

Graywacke Sandstone (C6H10O5)x - predominantly quartz and feldspar

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Dark grey to charcoal; Luster: Dull/Earthy; Crystal Structure: Clastic (fine to medium grained); Cleavage: None (subconchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6-7 on Mohs scale
Color: Dark grey to charcoal
Luster: Dull/Earthy

Identified June 10, 2026More sedimentary →

Explore Graywacke 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 on Mohs scale; Color: Dark grey to charcoal; Luster: Dull/Earthy; Crystal Structure: Clastic (fine to medium grained); Cleavage: None (subconchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed from the rapid deposition of poorly sorted sediment in deep marine environments, often associated with submarine avalanches or turbidity currents. Most specimens date from the Paleozoic or Mesozoic eras.

Uses & applications

Primarily used as high-quality road aggregate, railway ballast, and in heavy construction due to its hardness and durability. Occasionally used for decorative stone walls.

Geological facts

Graywacke is often called 'dirty sandstone' because of its high clay matrix content. It is a key indicator of ancient tectonic 'active margins' where mountains were rapidly eroding into deep ocean trenches.

Field identification & locations

Identify by its dark, muddy appearance and extreme hardness compared to other sandstones. It will not scratch easily with a steel knife. Commonly found in mountainous regions near old coastlines.