igneous
Granite or granitic gneiss cobble
Quartz–feldspar–biotite granitoid; possibly weakly foliated gneiss
AI-generated identification · may be incorrectCoarse, pale pink-gray, granular texture with quartz, feldspar, and minor dark mica; vitreous quartz and feldspar luster, no obvious cleavage in the whole rock. Typical hardness is about 6–7 Mohs and specific gravity 2.6–2.8.
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Physical properties
Coarse, pale pink-gray, granular texture with quartz, feldspar, and minor dark mica; vitreous quartz and feldspar luster, no obvious cleavage in the whole rock. Typical hardness is about 6–7 Mohs and specific gravity 2.6–2.8.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the continental crust, commonly during Precambrian to Phanerozoic mountain-building; if gneissic, it was later subjected to high-grade metamorphism. Weathering and transport rounded it into a cobble.
Uses & applications
Used as crushed aggregate, road stone, building stone, landscaping rock, and occasionally as a polished decorative slab. This ordinary outdoor cobble has little gem or collector premium.
Geological facts
The pink coloration usually comes from potassium feldspar, while gray translucent grains are quartz. Iron-oxide weathering can produce the rusty patches visible on the surface.
Field identification & locations
Identify it by its interlocking visible grains, pale feldspar, glassy quartz, and scattered dark mica; unlike sandstone, it lacks distinct sedimentary layers. Common in glacial deposits, stream gravels, and exposed continental crust.
