sedimentary
Sandstone (Graywacke)
Arenite / Graywacke (SiO2 with lithic fragments)
Hardness: 6-7 Mohs; Color: Gray, tan, or greenish-gray; Luster: Dull/Earthy; Crystal structure: Clastic (grainy texture); Cleavage: None (conchoidal fracture possible in fine grains); Specific Gravity: 2.2-2.8
- Hardness
- 6-7 Mohs
- Color
- Gray, tan, or greenish-gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Gray, tan, or greenish-gray; Luster: Dull/Earthy; Crystal structure: Clastic (grainy texture); Cleavage: None (conchoidal fracture possible in fine grains); Specific Gravity: 2.2-2.8
Formation & geological history
Formed from the accumulation and lithification of sand-sized mineral grains or rock fragments. Often deposited in marine environments or river beds; can range from Precambrian to Holocene in age.
Uses & applications
Commonly used in construction as an aggregate for road base, building stone, or in the manufacturing of glass if high in silica content.
Geological facts
Graywacke is often called 'dirty sandstone' because it contains a mix of poorly sorted grains and a clay matrix, indicating rapid deposition near its source.
Field identification & locations
Identify by its gritty, sandpaper-like texture and visible grains. Found worldwide in sedimentary basins and mountain ranges with exposed uplifted strata. Look for bedding planes or layering.
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