igneous
Granite
Granite; primarily quartz, alkali feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, speckled pink, white, gray, and black; interlocking crystals with vitreous to dull luster. Hardness is approximately 6–7 Mohs; no obvious cleavage as a whole rock, though feldspars cleave.
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Physical properties
Coarse-grained, speckled pink, white, gray, and black; interlocking crystals with vitreous to dull luster. Hardness is approximately 6–7 Mohs; no obvious cleavage as a whole rock, though feldspars cleave.
Formation & geological history
An intrusive felsic igneous rock formed by slow cooling of silica-rich magma deep in the crust, allowing large crystals to grow. Individual samples commonly formed during Precambrian to younger continental plutonic events.
Uses & applications
Widely used for building facades, countertops, monuments, paving, aggregate, and dimension stone; attractive pieces are collected but generally inexpensive.
Geological facts
The pink grains are likely potassium feldspar, translucent grains are quartz, and dark grains are biotite or amphibole. Its coarse texture distinguishes it from volcanic rhyolite, which cools too quickly for visible crystals.
Field identification & locations
Identify it by its granular, interlocking texture and mixed quartz-feldspar-dark-mineral coloration; it commonly occurs in continental mountain belts, plutons, and glacial deposits. A fresh surface and dilute acid test (no fizz) help distinguish it from carbonate rocks.
