igneous
Biotite granite (weathered granitic rock)
Granite; chiefly quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, mottled cream, gray, black, and brown; vitreous quartz, blocky feldspar, and shiny platy biotite. Hardness is roughly 6–7 for quartz and feldspar, with mica softer; no obvious layering or foliation is visible.
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Physical properties
Coarse-grained, mottled cream, gray, black, and brown; vitreous quartz, blocky feldspar, and shiny platy biotite. Hardness is roughly 6–7 for quartz and feldspar, with mica softer; no obvious layering or foliation is visible.
Formation & geological history
A plutonic igneous rock formed when silica-rich magma cooled slowly deep underground, allowing visible crystals to grow; commonly Paleozoic to Precambrian in exposed continental crust, though age varies by locality.
Uses & applications
Widely used as building stone, countertops, monuments, aggregate, and landscaping material; this small weathered specimen has mainly educational or modest collecting value.
Geological facts
The rusty brown areas likely represent weathered iron-bearing biotite or feldspar, while the dark grains are biotite and possibly hornblende. Granite is the coarse-grained equivalent of rhyolite.
Field identification & locations
Identify it by its interlocking visible crystals, pale feldspar, translucent gray quartz, and black mica, without fossils or sedimentary layering. Common worldwide in continental mountain belts and shields; a fresh broken surface shows the texture best.
