igneous
Granite or granitic gneiss
Granite; primarily quartz, feldspar, and mica (possibly weakly foliated gneiss)
AI-generated identification · may be incorrectCoarse-grained, speckled gray-white stone with dark biotite/hornblende; quartz has Mohs hardness 7, feldspar 6, and the rock has a glassy to dull luster, interlocking crystals, and no prominent cleavage as a whole.
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Physical properties
Coarse-grained, speckled gray-white stone with dark biotite/hornblende; quartz has Mohs hardness 7, feldspar 6, and the rock has a glassy to dull luster, interlocking crystals, and no prominent cleavage as a whole.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep underground, commonly during Precambrian to Phanerozoic mountain-building events; gneiss is its metamorphosed equivalent.
Uses & applications
Widely used for countertops, monuments, paving, aggregate, and building stone; attractive polished pieces have modest decorative or educational value.
Geological facts
Its visible grains indicate slow cooling rather than volcanic eruption. Dark minerals commonly weather faster, producing a rough, rusty surface.
Field identification & locations
Identify it by interlocking light quartz/feldspar grains and scattered dark mica; granite is common in continental shields and mountain ranges worldwide. A hand lens and streak, hardness, and acid tests help distinguish it from sandstone or concrete.
