igneous
Rounded granitic cobble
Granite to granodiorite; quartz–feldspar–mica aggregate
AI-generated identification · may be incorrectHardness about 6–7 Mohs; gray, white, and pink granular texture with dull to faintly vitreous luster. Interlocking crystals and poor cleavage as a whole; likely quartz, feldspar, and dark biotite or amphibole. Rounded and weathered by transport.
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Physical properties
Hardness about 6–7 Mohs; gray, white, and pink granular texture with dull to faintly vitreous luster. Interlocking crystals and poor cleavage as a whole; likely quartz, feldspar, and dark biotite or amphibole. Rounded and weathered by transport.
Formation & geological history
An intrusive igneous rock crystallized slowly from magma deep in the crust, commonly millions to billions of years ago. Its rounded shape indicates erosion and stream or glacial transport.
Uses & applications
Used as aggregate, road stone, building stone, monuments, and landscaping material; this small cobble has minimal commercial value.
Geological facts
The pink tones usually come from potassium feldspar, while gray or black grains may be quartz and biotite. A glassy quartz grain should resist scratching, whereas feldspar commonly shows cleavage.
Field identification & locations
Common in continental mountain regions and glacial deposits worldwide. Identify it by visible interlocking light and dark grains, high density, and inability to scratch it with a steel nail; exact identification requires a fresh surface or thin section.
