igneous
Biotite granite (weathered)
Granite, primarily quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, speckled brown-gray rock with granular texture and minor dark mica; quartz and feldspar have vitreous to dull luster, while mica is shiny and flaky. Hardness is approximately 6–7 overall; feldspar cleavage may be visible, and specific gravity is about 2.6–2.7.
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Physical properties
Coarse-grained, speckled brown-gray rock with granular texture and minor dark mica; quartz and feldspar have vitreous to dull luster, while mica is shiny and flaky. Hardness is approximately 6–7 overall; feldspar cleavage may be visible, and specific gravity is about 2.6–2.7.
Formation & geological history
An intrusive igneous rock formed when silica-rich magma cooled slowly deep underground, allowing large crystals to grow. Most granite formed during Precambrian to Phanerozoic continental crust-building events; the surface brown coloration likely reflects weathering.
Uses & applications
Widely used as building stone, countertops, monuments, paving, aggregate, and landscaping material. This hand specimen has modest collector value.
Geological facts
The visible granular texture records slow underground cooling. Brown staining commonly results from oxidation of iron-bearing biotite and weathering of feldspar.
Field identification & locations
Identify it by interlocking visible crystals of light quartz/feldspar and dark mica, with no layering or fossils; a streak test is usually white, and it will not react strongly with dilute hydrochloric acid. Common worldwide in continental mountain belts and exposed plutons.
