igneous
Coarse-grained granite or granitic gneiss
Granite; mainly quartz (SiO₂), feldspar, and mica; possible gneissic deformation
AI-generated identification · may be incorrectHardness about 6–7; gray to cream with black and brown mica, vitreous to pearly luster, interlocking crystalline texture, and no prominent cleavage as a whole. The foliated-looking patches may indicate gneiss rather than ordinary granite.
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Physical properties
Hardness about 6–7; gray to cream with black and brown mica, vitreous to pearly luster, interlocking crystalline texture, and no prominent cleavage as a whole. The foliated-looking patches may indicate gneiss rather than ordinary granite.
Formation & geological history
Crystallized slowly from silica-rich magma deep in the continental crust, commonly hundreds of millions to billions of years old; if gneissic, it was later altered by intense heat and pressure.
Uses & applications
Used as building stone, countertops, paving, aggregate, and monuments; attractive hand specimens have modest collector interest.
Geological facts
Visible quartz and feldspar grains, plus shiny mica flakes, are characteristic. Weathering rounds exposed boulders and can produce the smooth shape shown.
Field identification & locations
Identify it by its coarse interlocking grains, abundant pale feldspar/quartz, and dark mica; distinguish it from marble by the lack of sugary calcite reaction and from sandstone by its crystalline texture. Common worldwide in continental shields and mountain belts.
