sedimentary
Sandstone (Greywacke)
Arenite / Wacke (Mainly SiO2 with various lithic fragments)
Hardness: 6-7 (Mohs scale); Color: Dark grey to brownish-grey; Luster: Dull/Earthy; Crystal structure: Granular (clastic texture); Cleavage: None; Specific gravity: 2.6 - 2.7.
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey to brownish-grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey to brownish-grey; Luster: Dull/Earthy; Crystal structure: Granular (clastic texture); Cleavage: None; Specific gravity: 2.6 - 2.7.
Formation & geological history
Formed through the accumulation of sand-sized grains, often in deep-water marine environments (turbidity currents). The presence of poor sorting and matrix suggests a 'dirty' sandstone origin, likely Paleozoic or Mesozoic era.
Uses & applications
Used primarily as crushed stone for road construction, concrete aggregate, and sometimes as a building stone or for landscaping.
Geological facts
Greywacke is often called 'dirty sandstone' because of its high clay and rock fragment content. It often exhibits graded bedding, which tells geologists which way was 'up' when the rock formed millions of years ago.
Field identification & locations
Identify in the field by its gritty texture (feels like sandpaper), visible layering (bedding), and resistance to scratching. Common in mountain belts and coastal regions. Best for collectors when it contains fossils or distinct quartz veining.
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