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

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Fossilized shell fragment, likely bivalve

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fossil
Fossilized marine shell fragment (Likely a bivalve or gastropod shell preserved as calcite (CaCO₃)) — fossil

Fossilized marine shell fragment

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mineral
Granite with Epidote (Granite, containing quartz, feldspar, and epidote) — Igneous

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Biotite Mica Schist

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metamorphic
Fossiliferous limestone fragment (Calcitic limestone; mainly calcium carbonate (CaCO₃), possibly with shell or coral debris) — sedimentary

Fossiliferous limestone fragment

Calcitic limestone; mainly calcium carbonate (CaCO₃), possibly with shell or coral debris

sedimentary