sedimentary
Crushed Stone / Greywacke
Greywacke (Indurated Sandstone)
Hardness: 6-7 Mohs; Color: Dark grey to charcoal, sometimes greenish-grey; Luster: Dull or earthy; Structure: Clastic with a fine-grained matrix; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6-7 Mohs
- Color
- Dark grey to charcoal, sometimes greenish-grey
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to charcoal, sometimes greenish-grey; Luster: Dull or earthy; Structure: Clastic with a fine-grained matrix; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the rapid deposition of poorly sorted sediment in deep water environments like submarine fans. Usually associated with tectonic activity near continental margins.
Uses & applications
Predominantly used as crushed stone for road construction, railroad ballast, and concrete aggregate due to its high durability and hardness.
Geological facts
Greywacke is unique because it contains a significant amount of mud-sized particles alongside larger grains, indicating it was deposited very quickly by turbidity currents.
Field identification & locations
Identify by its dark color, toughness, and 'dirty' look under a lens (mix of sand and clay). Common in folded mountain belts and coastal ranges.
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