sedimentary
Graywacke with Quartz Vein
Lithic Sandstone (Graywacke)
Hardness: 6-7 (Mohs scale); Color: Dirty gray to brownish-green; Luster: Dull/Earthy; Structure: Clastic, fine to medium-grained; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 6-7 (Mohs scale)
- Color
- Dirty gray to brownish-green
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dirty gray to brownish-green; Luster: Dull/Earthy; Structure: Clastic, fine to medium-grained; Cleavage: None; 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. This specimen features a secondary quartz vein formed when silica-rich fluids filled a fracture long after the rock solidified.
Uses & applications
Used primarily as road base, railroad ballast, and coarse aggregate in construction; occasionally used for paving stones.
Geological facts
Graywacke is often called 'dirty sandstone' because of its high clay content and variety of rock fragments. It is a key indicator of ancient tectonic activity and underwater landslides.
Field identification & locations
Identify by its gray color, extreme hardness compared to other sandstones, and the presence of poorly sorted grains. Commonly found in coastal or mountainous regions with history of oceanic subduction.
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