igneous
Biotite-rich granite or granitic pegmatite
Coarse-grained granite, likely containing quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectHardness is approximately 6–7 for quartz and feldspar, with softer biotite near 2.5–3; it is dark gray to black with silvery reflective mica, granular texture, and vitreous to pearly luster. Interlocking crystals show no obvious layering or foliation.
Identified More igneous →
Explore Biotite-rich granite or granitic pegmatite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness is approximately 6–7 for quartz and feldspar, with softer biotite near 2.5–3; it is dark gray to black with silvery reflective mica, granular texture, and vitreous to pearly luster. Interlocking crystals show no obvious layering or foliation.
Formation & geological history
Formed when silica-rich magma cooled slowly underground, allowing large crystals to grow; likely Precambrian to younger depending on locality. The specimen may represent a pegmatitic or strongly porphyritic portion of a granite body.
Uses & applications
Granite is used as crushed stone, aggregate, dimension stone, countertops, and monuments; attractive mica-rich pieces are collected but generally have little commercial gem value.
Geological facts
The bright flakes are probably biotite or muscovite mica, while pale translucent grains are quartz and blocky white grains are feldspar. A hand lens can reveal mica’s sheet-like cleavage and quartz’s glassy, irregular fracture.
Field identification & locations
Common in continental crust and exposed in mountain belts, including the Sierra Nevada, Appalachians, Canadian Shield, and many granite terrains worldwide. Look for visible interlocking quartz, feldspar, and mica grains; a streak test is unhelpful because the minerals are too hard.
