igneous
Biotite granite (possibly pegmatitic granite)
Granite: quartz (SiO₂), feldspar (KAlSi₃O₈–NaAlSi₃O₈), and biotite mica
AI-generated identification · may be incorrectCoarse-grained, pinkish-white feldspar and quartz enclosed by black, platy biotite; vitreous quartz, pearly mica, and uneven fracture. Typical hardness is 6–7 for quartz/feldspar and 2.5–3 for biotite; specific gravity is about 2.6–2.8.
Identified More igneous →
Explore Biotite granite (possibly pegmatitic granite) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse-grained, pinkish-white feldspar and quartz enclosed by black, platy biotite; vitreous quartz, pearly mica, and uneven fracture. Typical hardness is 6–7 for quartz/feldspar and 2.5–3 for biotite; specific gravity is about 2.6–2.8.
Formation & geological history
Forms when silica-rich magma slowly cools and crystallizes deep in the crust, commonly during Precambrian to Phanerozoic mountain-building events. The specimen appears freshly broken or partially weathered rather than polished.
Uses & applications
Used widely as building stone, countertops, monuments, aggregate, and crushed stone; attractive pieces may be collected but are generally low-value.
Geological facts
The black mineral is likely biotite, whose cleavage produces shiny flakes; the salmon-pink component is commonly potassium feldspar. Exact identification would benefit from a close-up and hardness or streak tests.
Field identification & locations
Recognize interlocking visible crystals, pink/white feldspar, translucent quartz, and black mica; common in continental crust, granite quarries, and glacial deposits worldwide. Estimated value: $1–$10 for a small ordinary fragment, or $10–$30 if unusually attractive or locality-labeled.
