Greywacke is a hard, grey to greyish-green sandstone in which sand grains are embedded in a fine clay- and mud-like matrix. It is a sedimentary rock that, because of its hardness and strength, is widely used as road-building stone, aggregate and building stone.
Formation and properties
Greywacke formed when turbid underwater currents deposited sand, clay and rock particles all at once. As a result it is poorly sorted: coarse and fine particles lie mixed together. Characteristic features are:
- Hard and strong — high compressive and wear strength
- Grey colour — from light grey to dark greyish-green
- Compact, dense structure — few pores, good frost resistance
Application
- Road building — as crushed stone and aggregate in asphalt and foundation layers, because of its high wear resistance
- Concrete — as coarse aggregate
- Building stone — historically used for walls, bridges and water works in areas where the rock occurs
- Rip-rap and armour stone — in bank and water works
Point of attention
The quality differs from one quarry to another. For use as aggregate, the grading, hardness and frost resistance are decisive.
Related Terms
- Natural stone
- Sedimentary rock
- Aggregate
- Rubble stone
- Granite
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