igneous
Biotite-rich granite or granodiorite
Coarse-grained granitoid, primarily quartz, plagioclase/feldspar, and biotite mica
AI-generated identification · may be incorrectHardness about 6–7; dark gray-brown, speckled, and granular with a dull to vitreous luster. Interlocking crystals are visible, with possible mica flakes and irregular fracture; no obvious foliation.
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Physical properties
Hardness about 6–7; dark gray-brown, speckled, and granular with a dull to vitreous luster. Interlocking crystals are visible, with possible mica flakes and irregular fracture; no obvious foliation.
Formation & geological history
An intrusive igneous rock that crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic mountain-building events. Exact age and classification require thin-section or chemical analysis.
Uses & applications
Used as crushed aggregate, road stone, building stone, and sometimes decorative dimension stone. This rough specimen has modest collector value.
Geological facts
Its dark appearance may reflect abundant biotite, hornblende, or weathering; the photograph alone cannot reliably distinguish granite from granodiorite or diorite.
Field identification & locations
Identify it by coarse interlocking grains, abundant light feldspar/quartz, and dark mica or amphibole; it should not fizz with dilute acid. Common worldwide in continental batholiths and mountain belts.
