igneous
Granite (rounded glacial cobble)
Granite; predominantly quartz, alkali feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, speckled gray-pink-black appearance with interlocking crystals; quartz hardness 7 and feldspar about 6, overall Mohs hardness roughly 6–7. Typically has a granular texture, vitreous quartz luster, and no prominent cleavage as a whole rock.
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Physical properties
Coarse-grained, speckled gray-pink-black appearance with interlocking crystals; quartz hardness 7 and feldspar about 6, overall Mohs hardness roughly 6–7. Typically has a granular texture, vitreous quartz luster, and no prominent cleavage as a whole rock.
Formation & geological history
A felsic intrusive igneous rock crystallized slowly from magma deep in the crust, commonly during Precambrian to Phanerozoic mountain-building events. Its rounded form likely resulted from glacial transport or prolonged stream abrasion.
Uses & applications
Widely used as dimension stone, countertops, monuments, paving, aggregate, and decorative landscaping rock; this specimen is mainly of modest collecting interest.
Geological facts
The visible black minerals are likely biotite or amphibole, while pale translucent grains are quartz and feldspar. Pink coloration commonly reflects potassium feldspar.
Field identification & locations
Identify it by its coarse interlocking crystals and gray-pink-black speckling; unlike gneiss, it lacks consistent compositional banding. Common worldwide, especially in exposed continental crust and glacial deposits.
