igneous
Mica-rich granite or granitic pegmatite
Biotite granite; primarily quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, cream to gray rock with black, reflective biotite flakes and likely white potassium feldspar/quartz; hardness about 6–7, vitreous to pearly luster, no consistent cleavage as a whole, and specific gravity roughly 2.6–2.8.
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Physical properties
Coarse-grained, cream to gray rock with black, reflective biotite flakes and likely white potassium feldspar/quartz; hardness about 6–7, vitreous to pearly luster, no consistent cleavage as a whole, and specific gravity roughly 2.6–2.8.
Formation & geological history
A plutonic igneous rock formed by slow cooling and crystallization of silica-rich magma deep underground, generally during Precambrian to Phanerozoic mountain-building events; the exact age requires laboratory analysis.
Uses & applications
Commonly used as crushed aggregate, building stone, countertops, and monuments; attractive hand specimens are collected but are usually inexpensive.
Geological facts
The black patches are most likely biotite, while the pale matrix is feldspar and quartz. The image does not clearly show enough crystal detail to distinguish ordinary granite from a pegmatitic or gneissic variant.
Field identification & locations
Identify it by its interlocking coarse grains, pale feldspar/quartz matrix, and abundant dark mica; unlike gneiss, it lacks obvious continuous foliation or banding. Similar material occurs worldwide, especially in granitic mountain belts.
