igneous
Coarse-grained granite (likely granitic beach rock)
Granite; chiefly quartz (SiO₂), feldspar, and mica/amphibole
AI-generated identification · may be incorrectHardness about 6–7 Mohs; speckled gray, white, black, and tan appearance with a coarse crystalline texture and mostly vitreous-to-pearly luster. Interlocking crystals show no obvious cleavage as a whole, though feldspar and mica have cleavage.
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Physical properties
Hardness about 6–7 Mohs; speckled gray, white, black, and tan appearance with a coarse crystalline texture and mostly vitreous-to-pearly luster. Interlocking crystals show no obvious cleavage as a whole, though feldspar and mica have cleavage.
Formation & geological history
Intrusive igneous rock formed by slow cooling and crystallization of silica-rich magma deep in Earth’s crust, typically during Precambrian to Phanerozoic continental mountain-building. Weathering and wave action produced the rounded beach fragment.
Uses & applications
Widely used as crushed aggregate, building stone, countertops, monuments, and decorative landscaping material; attractive hand specimens are collected but generally inexpensive.
Geological facts
The visible black grains are likely biotite mica or hornblende, while pale grains are feldspar and translucent grains may be quartz. Granite’s large crystals indicate slow underground cooling rather than volcanic eruption.
Field identification & locations
Identify it by its visibly interlocking quartz, feldspar, and dark mafic minerals; it is common in continental crust and glacial or coastal gravels worldwide. Exact identification would benefit from a fresh surface, hardness testing, and magnification.
