sedimentary
Greywacke
Lithic Wacke
Hardness: 6-7 on Mohs scale; Color: Grey to dark grey/greenish; Luster: Dull/Earthy; Structure: Clastic, fine to coarse-grained with a dense matrix; Cleavage: None
- Hardness
- 6-7 on Mohs scale
- Color
- Grey to dark grey/greenish
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Grey to dark grey/greenish; Luster: Dull/Earthy; Structure: Clastic, fine to coarse-grained with a dense matrix; Cleavage: None
Formation & geological history
Formed from rapid deposition of poorly sorted sediment in deep ocean basins, often via turbidity currents. Generally found in Paleozoic to Mesozoic orogenic belts.
Uses & applications
Used primarily in construction as road base, concrete aggregate, and railroad ballast. Due to its durability, it is also used for paving stones.
Geological facts
Greywacke is often called 'dirty sandstone' because of its high content of clay and rock fragments. It is a key indicator of ancient submarine landslide events called turbidites.
Field identification & locations
Identify in the field by its dark color, extreme hardness compared to other sandstones, and poorly sorted grains that are not easily visible without a lens. Common in coastal mountain ranges.
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