igneous
Granite cobble
Granite; chiefly quartz (SiO₂), feldspar, and mica/amphibole
AI-generated identification · may be incorrectCoarse-grained, speckled white-gray rock with dark biotite or amphibole and rusty iron staining; typically Mohs 6–7, vitreous quartz luster, interlocking crystals, and no cleavage as a whole. The rounded shape indicates water or glacial abrasion.
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Physical properties
Coarse-grained, speckled white-gray rock with dark biotite or amphibole and rusty iron staining; typically Mohs 6–7, vitreous quartz luster, interlocking crystals, and no cleavage as a whole. The rounded shape indicates water or glacial abrasion.
Formation & geological history
An intrusive felsic igneous rock crystallized slowly from magma deep in Earth’s crust, commonly during Precambrian to Phanerozoic continental activity; later weathering produced this cobble.
Uses & applications
Used as dimension stone, countertops, paving, aggregate, monuments, and landscaping; this rounded specimen has modest collecting value.
Geological facts
Granite’s visible crystals formed because underground magma cooled slowly. Dark bands or patches may represent biotite-rich schlieren, amphibolite inclusions, or weathered veins rather than true layering.
Field identification & locations
Identify it by its interlocking quartz-feldspar-mica texture, hardness, and lack of pore spaces; common in continental mountain belts and stream or glacial gravels worldwide. A hand lens and streak/acid tests help distinguish it from gneiss or quartzite.
