sedimentary
River Stone (Greywacke)
Greywacke (immature sandstone)
Hardness: 6-7 on Mohs scale; Color: Dull grey to greenish-grey; Luster: Matte/earthy; Texture: Fine to medium-grained; Structure: Compact and dense with some visible light-colored mineral streaks.
- Hardness
- 6-7 on Mohs scale
- Color
- Dull grey to greenish-grey
- Luster
- Matte/earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dull grey to greenish-grey; Luster: Matte/earthy; Texture: Fine to medium-grained; Structure: Compact and dense with some visible light-colored mineral streaks.
Formation & geological history
Formed by the rapid deposition of poorly sorted sands, silts, and clays in deep marine environments/turbidity currents. Its rounded shape is the result of mechanical weathering and water erosion in a river or beach environment.
Uses & applications
Commonly used as decorative landscaping stone, in construction aggregates, or as base material for roads and drainage systems.
Geological facts
Greywacke is often called 'dirty sandstone' because of its poorly sorted nature and high clay content. It is extremely common in ancient mountain belts and tectonic subduction zones.
Field identification & locations
Identified by its dull grey color, durability, and smooth, water-worn texture. It is a ubiquitous finding in riverbeds and coastal areas globally.
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