igneous
Biotite-bearing granite or granitic pegmatite fragment
Granite/pegmatite; quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectDark gray, coarse-grained, uneven specimen with a brown translucent area likely weathered feldspar or quartz. Hardness is approximately 2.5–3 for biotite and 6–7 for quartz/feldspar; luster ranges from vitreous to pearly, with no reliable cleavage visible at this scale.
Identified More igneous →
Explore Biotite-bearing granite or granitic pegmatite fragment in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, coarse-grained, uneven specimen with a brown translucent area likely weathered feldspar or quartz. Hardness is approximately 2.5–3 for biotite and 6–7 for quartz/feldspar; luster ranges from vitreous to pearly, with no reliable cleavage visible at this scale.
Formation & geological history
Forms when silica-rich magma slowly crystallizes underground, typically during Precambrian to Phanerozoic continental crust formation. The dark surface may reflect mica-rich alteration or weathering.
Uses & applications
Common granite is used for construction aggregate, dimension stone, and countertops; attractive fragments may be collected but are generally not gem-quality.
Geological facts
The specimen appears heterogeneous rather than a single crystal, with flaky dark mica surrounding a brown central mineral. A scratch test and fresh broken surface would improve identification.
Field identification & locations
Look for interlocking quartz, feldspar, and shiny black biotite flakes; granite commonly occurs in continental plutons worldwide. Common localities include the United States, Canada, Brazil, India, and Scandinavia.
