igneous and metamorphic

Glacial Cobbles (predominantly Granite and Gneiss)

Mixed lithologies (Quartz, Feldspar, Mica assemblage)

AI-generated identification · may be incorrect

Hardness 6-7 (Mohs), varying colors including pink (feldspar-rich), grey, and black. Polgranular texture, crystalline luster, and rounded to sub-angular shapes from water/ice abrasion.

Identified June 19, 2026More igneous and metamorphic →

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Physical properties

Hardness 6-7 (Mohs), varying colors including pink (feldspar-rich), grey, and black. Polgranular texture, crystalline luster, and rounded to sub-angular shapes from water/ice abrasion.

Formation & geological history

These are glacial erratics or river cobbles. They formed deep in the crust millions to billions of years ago and were transported and rounded by glaciers or high-energy water movement during the Pleistocene era.

Uses & applications

Construction aggregate, landscaping decor, erosion control (riprap), and geological study.

Geological facts

Glacial cobbles often travel hundreds of miles from their parent bedrock. One rock in a pile might be 2 billion years old next to one that is only 500 million years old.

Field identification & locations

Look for rounded edges and mixed mineral grains. Commonly found in 'till' plains, riverbeds, and glacial moraines across the northern US, Canada, and Northern Europe.