Sandstone (Greywacke)

Physical Properties

Hardness: 6-7 Mohs; Color: Grey to brownish-grey; Luster: Dull/Earthy; Structure: Fine-grained clastic texture with visible sand particles; Cleavage: None; Specific Gravity: 2.2-2.8.

Formation & Geological History

Formed through the accumulation and lithification of sand-sized mineral particles or rock fragments. This specific specimen appears water-worn, likely shaped by river or coastal erosion over thousands of years.

Uses & Applications

Commonly used in construction as aggregate, for paving, or as a decorative landscaping stone. Very fine-grained varieties can be used as whetstones for sharpening tools.

Geological Facts

Greywacke is often called 'dirty sandstone' because it contains a mix of poorly sorted grains and a clay matrix. It is frequently associated with deep-marine environments or submarine fans.

Field Identification & Locations

Identify by its gritty texture (feels like sandpaper) and visible small mineral grains. It is extremely common in riverbeds and mountainous regions where ancient seabeds have been uplifted.

Identified on: 4/21/2026

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