igneous
Biotite–hornblende granite (likely granodiorite)
Coarse crystalline plutonic rock composed mainly of quartz (SiO₂), feldspar, biotite mica, and amphibole
AI-generated identification · may be incorrectHardness about 6–7; dark gray to brown-black, granular, with vitreous quartz and sparkly mica; massive texture and no obvious cleavage as a whole, though mica has perfect basal cleavage. Specific gravity is typically 2.65–2.75.
Identified More igneous →
Explore Biotite–hornblende granite (likely granodiorite) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness about 6–7; dark gray to brown-black, granular, with vitreous quartz and sparkly mica; massive texture and no obvious cleavage as a whole, though mica has perfect basal cleavage. Specific gravity is typically 2.65–2.75.
Formation & geological history
Formed when silica-rich magma cooled slowly underground, allowing visible crystals to grow; commonly Paleozoic to Precambrian in exposed continental crust, though age depends on locality.
Uses & applications
Used as crushed aggregate, dimension stone, paving, and monuments; attractive polished pieces are collectible but generally low-value.
Geological facts
The dark minerals are likely biotite and/or hornblende, while pale grains are feldspar and quartz. Exact identification requires a fresh surface, mineral proportions, and ideally thin-section or chemical analysis.
Field identification & locations
Common in continental mountain belts and shield regions worldwide, including the Sierra Nevada, Canadian Shield, Scandinavia, and Appalachians. Look for interlocking visible crystals, hard quartz, feldspar cleavage, and mica flakes; it is not reliably distinguishable from granodiorite by sight alone.
