sedimentary
Greyling Sandstone / Greywacke
Lithic Wacke (SiO2 + diverse mineral fragments)
Hardness: 6-7 (Mohs scale); Color: Dark grey to greenish-grey; Luster: Dull to earthy; Texture: Fine to medium-grained; Structure: Poorly sorted clastic grains in a clay-rich matrix; Specific Gravity: 2.6-2.7.
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey to greenish-grey
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey to greenish-grey; Luster: Dull to earthy; Texture: Fine to medium-grained; Structure: Poorly sorted clastic grains in a clay-rich matrix; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through rapid deposition in deep-marine environments (turbidite deposits), typically near continental margins or volcanic islands. Often found in Paleozoic to Mesozoic orogenic belts.
Uses & applications
Primarily used as crushed stone for road construction, railroad ballast, and concrete aggregate. Occasionally used as flagging or paving stones due to its durability.
Geological facts
Greywacke is often called 'dirty sandstone' because of its high clay content and poor sorting. It is a major component of the geological record in mountain-building zones like the Appalachians or the New Zealand Alps.
Field identification & locations
Identify by its 'salt and pepper' appearance and extreme hardness compared to common siltstones. It usually lacks defined bedding in small hand samples. Found globally in folded mountain belts and coastal regions.
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