sedimentary
Graywacke
Lithic Sandstone (Graywacke)
Hardness: 6-7 on Mohs scale; Color: Dark gray to greenish-gray; Luster: Dull/Earthy; Structure: Fine-to-coarse grained clastic; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 6-7 on Mohs scale
- Color
- Dark gray to greenish-gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark gray to greenish-gray; Luster: Dull/Earthy; Structure: Fine-to-coarse grained clastic; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed from rapid deposition of poorly sorted sediment in deep-sea trenches or underwater landslides (turbidity currents). Common in orogenic belts where tectonic plates collide.
Uses & applications
Primarily used as construction aggregate, road base, and ballast due to its durability and hardness.
Geological facts
Graywacke is often called 'dirty sandstone' because it contains a mix of sand-sized grains and a fine-grained clay matrix. It is a key indicator of past submarine landslide activity.
Field identification & locations
Identify by its dark, muddy color and the presence of angular rock fragments and quartz within a dense matrix. Commonly found along coastal areas and folded mountain chains.
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