igneous
Coarse-grained granite or granitic pegmatite
Granite; primarily quartz (SiO₂), feldspar, and mica/amphibole
AI-generated identification · may be incorrectHardness about 6–7 Mohs; mottled gray, cream, black, and pink with a coarse crystalline texture. Crystals are interlocking, with glassy quartz, blocky feldspar, and dark platy or prismatic minerals; cleavage occurs in feldspar and mica, but not quartz.
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Physical properties
Hardness about 6–7 Mohs; mottled gray, cream, black, and pink with a coarse crystalline texture. Crystals are interlocking, with glassy quartz, blocky feldspar, and dark platy or prismatic minerals; cleavage occurs in feldspar and mica, but not quartz.
Formation & geological history
An intrusive igneous rock that crystallized slowly from silica-rich magma deep in the crust, likely during a Precambrian or younger plutonic event; the exact age cannot be determined from the photograph.
Uses & applications
Widely used as building stone, countertops, monuments, aggregate, and decorative material; attractive crystals may have modest collector value.
Geological facts
The large visible crystals indicate slow underground cooling rather than volcanic eruption. Dark grains may be biotite mica or amphibole, while pale grains are probably feldspar and quartz.
Field identification & locations
Identify it by its coarse interlocking crystals and lack of layering or foliation; a glassy quartz grain will not show cleavage, whereas feldspar commonly breaks along flat planes. Common worldwide in continental mountain belts and exposed plutons.
