sedimentary
Sandstone (Greywacke)
Arenite / Lithic Wacke (SiO2 predominant)
Hardness: 6.5-7 (Mohs); Color: Dull grey, tan, and olive green; Luster: Earthy to dull; Crystal structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Dull grey, tan, and olive green
- Luster
- Earthy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Dull grey, tan, and olive green; Luster: Earthy to dull; Crystal structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments, often in marine environments or riverbeds where tectonic activity deposits poorly sorted sediment. This specimen appears water-worn into a pebble shape.
Uses & applications
Common greywacke is used extensively as road base, construction aggregate, and in heavy engineering projects due to its extreme hardness and durability.
Geological facts
Greywacke is often called 'dirty sandstone' because it contains a mix of different sized particles and a clay matrix. It is frequently associated with deep-sea fan deposits called turbidites.
Field identification & locations
Identify by its gritty texture and lack of visible layering in small pebbles. It is commonly found in riverbeds, glacial tills, and coastal areas associated with mountain building ranges.
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