igneous
Glacial Cobble with Granite Inclusion
Porphyritic Basalt or Andesite containing Granitic Xenolith
Hardness 6-7 Mohs; Color: dark grey/green matrix with a prominent pink/salmon inclusion; Luster: matte/earthy; Crystal structure: fine-grained (aphanitic) matrix with coarse-grained (phaneritic) inclusion; Shape: water-worn, rounded cobble.
- Luster
- matte/earthy
Identified More igneous →
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Physical properties
Hardness 6-7 Mohs; Color: dark grey/green matrix with a prominent pink/salmon inclusion; Luster: matte/earthy; Crystal structure: fine-grained (aphanitic) matrix with coarse-grained (phaneritic) inclusion; Shape: water-worn, rounded cobble.
Formation & geological history
Formed through volcanic activity where a fragment of older granite was caught in rising magma (xenolith). It was subsequently eroded and transported by glacial or fluvial processes, which accounts for its smooth, rounded shape. Age varies by region but often associated with Precambrian or Paleozoic formations.
Uses & applications
Primarily used as decorative landscaping stone or river rock. It holds educational value for demonstrating geological concepts like xenoliths and glacial transport.
Geological facts
The pink inclusion is a 'xenolith', a piece of pre-existing rock that did not melt but became trapped inside a different igneous rock body as it cooled. This specimen demonstrates two distinct cooling rates in one stone.
Field identification & locations
Look for a smooth, rounded grey or dark green rock that contains a sharp-bordered, differently colored and textured mineral patch. Commonly found in glacial till areas, riverbeds, and Great Lakes shorelines.
