sedimentary
River Stone (Greywacke)
Greywacke (Lithic Sandstone)
Hardness: 6-7 (Mohs); Color: Grey, greenish-grey, or brownish; Luster: Dull/Earthy; Structure: Massive, fine to medium-grained; Cleavage: None.
- Hardness
- 6-7 (Mohs)
- Color
- Grey, greenish-grey, or brownish
- Luster
- Dull/Earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs); Color: Grey, greenish-grey, or brownish; Luster: Dull/Earthy; Structure: Massive, fine to medium-grained; Cleavage: None.
Formation & geological history
Formed in deep-water marine environments from the rapid deposition of poorly sorted sand, mud, and rock fragments. This specimen has been rounded by fluvial (river) erosion over thousands of years.
Uses & applications
Used primarily in construction aggregate, road base, landscaping, and as decorative river rock in gardens.
Geological facts
Greywacke is often called 'dirty sandstone' because of its high clay and rock fragment content. It often indicates high tectonic activity at the time of its formation.
Field identification & locations
Identify by its salt-and-pepper appearance, dull grey color, and extreme hardness. Commonly found in riverbeds, glacial deposits, and coastal areas.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary