igneous
Granite (likely weathered biotite granite)
Coarse-grained felsic plutonic rock composed mainly of quartz, alkali feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectLight gray, speckled black-and-white, granular texture with an equigranular crystalline structure; vitreous quartz and feldspar luster, no obvious cleavage as a whole, Mohs hardness about 6–7, specific gravity roughly 2.63–2.75.
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Physical properties
Light gray, speckled black-and-white, granular texture with an equigranular crystalline structure; vitreous quartz and feldspar luster, no obvious cleavage as a whole, Mohs hardness about 6–7, specific gravity roughly 2.63–2.75.
Formation & geological history
Formed when silica-rich magma slowly crystallized deep underground, commonly during Precambrian to Phanerozoic mountain-building events; surface weathering rounded the specimen.
Uses & applications
Widely used for countertops, monuments, building stone, paving, aggregate, and landscaping; attractive pieces are collected but generally have modest value.
Geological facts
The black grains are likely biotite or hornblende, while translucent gray grains are quartz and pale grains are feldspar. Granite’s visible interlocking crystals indicate slow cooling rather than volcanic eruption.
Field identification & locations
Identify it by its coarse interlocking grains, abundant pale feldspar, gray quartz, and scattered dark mica/amphibole; it is common in continental shields and mountain belts worldwide. A precise identification would require a fresh surface or thin section.
