igneous and metamorphic
Glacial Cobbles (predominantly Granite and Gneiss)
Mixed lithologies (Quartz, Feldspar, Mica assemblage)
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.
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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.
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