Greywacke (River Slikenside)

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Dull grey to greenish-grey with yellowish mineral veins; Luster: Dull/Earthy; Crystal structure: Clastic (fine to medium grain); Cleavage: None; Specific gravity: 2.6-2.7

Formation & Geological History

Formed in deep-water marine environments (turbidity currents) where sand, mud, and rock fragments are deposited rapidly. This specimen has been rounded by river or glacial erosion, potentially during the Cenozoic era or older.

Uses & Applications

Primarily used as a heavy-duty construction aggregate, road base, or railroad ballast due to its hardness and durability.

Geological Facts

Greywacke is often called 'dirty sandstone' because it contains a wide variety of unsorted mineral fragments and a muddy matrix. It is a major component of mountain belts like the Appalachians and the Alps.

Field Identification & Locations

Identify by its 'salt and pepper' appearance and extreme hardness compared to other sandstones. Often found in riverbeds near tectonic uplift zones. Collectors value smooth, water-worn specimens as 'river stones' or 'worry stones'.

Identified on: 4/20/2026

Mode: Standard