sedimentary

Glacial Erratic (Graywacke/Sandstone)

Clastic Sedimentary Rock (Lithic Sandstone)

AI-generated identification · may be incorrect

Hardness: 6-7 Mohs; Color: Light gray to tan with weathering rinds; Luster: Dull/Earthy; Structure: Clastic, fine to medium-grained; Cleavage: None

Hardness: 6-7 Mohs
Color: Light gray to tan with weathering rinds
Luster: Dull/Earthy

Identified July 10, 2026More sedimentary →

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Physical properties

Hardness: 6-7 Mohs; Color: Light gray to tan with weathering rinds; Luster: Dull/Earthy; Structure: Clastic, fine to medium-grained; Cleavage: None

Formation & geological history

Formed from the lithification of sand, silt, and clay in marine or river environments, then transported and smoothed by glacial movement during the Pleistocene epoch.

Uses & applications

Commonly used as landscaping stones, fill material in construction, or riprap for erosion control.

Geological facts

These rounded boulders are often called 'erratics' if they differ in composition from the local bedrock, having been carried hundreds of miles by ice sheets.

Field identification & locations

Identify by its rounded, sub-angular shape and lack of visible layering compared to local shale. Common in glacial till deposits across North America and Europe.