igneous
Rounded granite cobble
Granite, typically quartz–alkali feldspar–plagioclase with minor biotite or amphibole
AI-generated identification · may be incorrectCoarse-grained, speckled gray-pink appearance with interlocking crystals; quartz gives a glassy luster, feldspar a pale/white to pink color, and dark minerals produce flecks. Hardness is approximately 6–7 Mohs; massive, without cleavage as a whole, and dense (about 2.6–2.8 specific gravity).
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Physical properties
Coarse-grained, speckled gray-pink appearance with interlocking crystals; quartz gives a glassy luster, feldspar a pale/white to pink color, and dark minerals produce flecks. Hardness is approximately 6–7 Mohs; massive, without cleavage as a whole, and dense (about 2.6–2.8 specific gravity).
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in continental crust, commonly during Precambrian to Phanerozoic plutonic events. Its rounded shape likely formed by stream, glacial, or landscaping abrasion.
Uses & applications
Widely used for countertops, monuments, building stone, paving, road aggregate, and decorative landscaping; generally little gemstone value.
Geological facts
The visible grains are interlocking crystals large enough to see without magnification, distinguishing granite from volcanic rhyolite. Surface weathering can oxidize biotite or iron-bearing minerals to brownish patches.
Field identification & locations
Identify it by visible quartz, light feldspar, and scattered dark mica/amphibole grains, plus strong resistance to scratching with a steel knife. Common worldwide, especially in continental mountain belts and glacial or river deposits.
