igneous
Biotite-bearing granite or granitic gneiss
Quartz–feldspar–mica aggregate; likely granite, possibly weakly metamorphosed gneiss
AI-generated identification · may be incorrectCoarse-grained, irregular specimen with pale gray/cream feldspar and quartz plus black biotite or hornblende. Typical hardness is about 6–7 Mohs, with vitreous quartz, dull feldspar, and platy mica cleavage; no clear crystal faces are visible.
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Physical properties
Coarse-grained, irregular specimen with pale gray/cream feldspar and quartz plus black biotite or hornblende. Typical hardness is about 6–7 Mohs, with vitreous quartz, dull feldspar, and platy mica cleavage; no clear crystal faces are visible.
Formation & geological history
Formed by slow cooling of silica-rich magma deep underground, generally in Precambrian to Phanerozoic continental crust; if gneissic, it was later recrystallized under high heat and pressure.
Uses & applications
Used as dimension stone, aggregate, monuments, countertops, and landscaping rock; small pieces have modest educational or collection value.
Geological facts
Granite commonly contains interlocking quartz and feldspar grains, while dark mica produces the black patches and flakes. The image alone cannot reliably distinguish granite from granitic gneiss.
Field identification & locations
Look for visible quartz, blocky feldspar, and shiny black mica; a glassy scratch-resistant quartz grain and light-colored streak are useful clues. Common worldwide, especially in continental shields and mountain belts.
