igneous
Biotite-bearing granite
Granite, composed chiefly of quartz, feldspar, and dark biotite or amphibole
AI-generated identification · may be incorrectCoarse-grained, mottled tan, gray, and black; visible interlocking crystals with vitreous to dull luster. Quartz is Mohs 7 and feldspar about 6; exact mineral proportions and density cannot be determined from the photo.
Identified More igneous →
Explore Biotite-bearing granite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse-grained, mottled tan, gray, and black; visible interlocking crystals with vitreous to dull luster. Quartz is Mohs 7 and feldspar about 6; exact mineral proportions and density cannot be determined from the photo.
Formation & geological history
Forms when silica-rich magma cools slowly underground, allowing large crystals to grow. Granite occurs in crust of many ages, from ancient Precambrian bodies to younger intrusions.
Uses & applications
Used as building and paving stone, aggregate, monuments, and decorative stone; this rough specimen is mainly suitable for collecting or teaching.
Geological facts
The contrasting light and dark patches reflect different minerals crystallizing together; the image alone does not establish a precise granite variety.
Field identification & locations
Identify by its coarse interlocking grains and mix of light quartz/feldspar with dark mica or amphibole. Common in continental mountain belts and exposed plutons worldwide; inspect a fresh surface for confirmation.
