igneous
Biotite granite (likely weathered granite)
Granite; quartz + feldspar + biotite, with accessory dark minerals
AI-generated identification · may be incorrectCoarse-grained, speckled tan, white, gray, and black rock with a granular texture; quartz has Mohs hardness 7, feldspar 6, and biotite 2.5–3, producing mixed hardness and weak mica cleavage; overall luster is mostly dull to subtly vitreous.
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Physical properties
Coarse-grained, speckled tan, white, gray, and black rock with a granular texture; quartz has Mohs hardness 7, feldspar 6, and biotite 2.5–3, producing mixed hardness and weak mica cleavage; overall luster is mostly dull to subtly vitreous.
Formation & geological history
A felsic intrusive igneous rock formed by slow cooling of silica-rich magma deep in the crust, allowing visible crystals to grow. Its precise age is unknown from the image and may range from Precambrian to Cenozoic depending on locality.
Uses & applications
Widely used as dimension stone, countertops, paving, monuments, aggregate, and crushed stone; attractive pieces may be sold as lapidary or teaching specimens.
Geological facts
The black flakes are likely biotite mica, while pale crystals are feldspar and translucent grains are quartz. Weathering commonly produces tan or rusty staining from iron-bearing minerals.
Field identification & locations
Identify it by its interlocking visible crystals, abundant pale feldspar/quartz, and black mica or hornblende; unlike basalt, it is light-colored and coarse-grained. Common in continental mountain belts and exposed granite plutons worldwide.
