igneous
Granite pebble
Granite; chiefly quartz (SiO₂), feldspar, and mica or amphibole
AI-generated identification · may be incorrectCoarse-grained, speckled white-gray-black appearance with interlocking crystals; quartz hardness 7, feldspar 6–6.5, mica about 2–3. Nonmetallic luster and generally no cleavage as a rock, though individual minerals cleave.
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Physical properties
Coarse-grained, speckled white-gray-black appearance with interlocking crystals; quartz hardness 7, feldspar 6–6.5, mica about 2–3. Nonmetallic luster and generally no cleavage as a rock, though individual minerals cleave.
Formation & geological history
Intrusive igneous rock formed when silica-rich magma cooled slowly deep underground, allowing visible crystals to grow. Most granite formed during Precambrian–Phanerozoic continental crust formation; this rounded piece was likely shaped by weathering and transport.
Uses & applications
Widely used as dimension stone, countertops, monuments, paving, aggregate, and landscaping stone. Ordinary pebbles have minimal commercial or jewelry value.
Geological facts
The black grains are commonly biotite mica or hornblende, while the glassy gray grains are quartz. Its granular texture distinguishes it from fine-grained volcanic rocks such as rhyolite.
Field identification & locations
Identify by visible interlocking white/pink feldspar, gray quartz, and black mica or amphibole; it is hard, dense, and does not fizz with dilute hydrochloric acid. Common worldwide, especially in continental shields and mountain belts.
