igneous
Quartz-rich granite or granitic gneiss
Granite; primarily quartz (SiO₂), feldspar, and biotite/amphibole
AI-generated identification · may be incorrectCoarse-grained, speckled tan-gray rock with abundant pale feldspar/quartz and dark mafic minerals; generally vitreous quartz luster, Mohs hardness about 6–7, poor cleavage as a whole, and specific gravity around 2.6–2.7. The rounded shape appears natural or water-worn.
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Physical properties
Coarse-grained, speckled tan-gray rock with abundant pale feldspar/quartz and dark mafic minerals; generally vitreous quartz luster, Mohs hardness about 6–7, poor cleavage as a whole, and specific gravity around 2.6–2.7. The rounded shape appears natural or water-worn.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the crust, producing visible interlocking crystals; comparable rocks formed mainly during Precambrian to Paleozoic continental crust development. Around 45.4°N, 73.3°W, glacially transported Canadian Shield granitic erratics are plausible.
Uses & applications
Commonly used as crushed stone, aggregate, building stone, monuments, countertops, and landscaping material; attractive polished pieces have modest decorative value.
Geological facts
The pale grains are likely feldspar and quartz, while black flakes or patches are biotite or hornblende. A photograph cannot reliably distinguish granite from granitic gneiss without seeing foliation or fabric.
Field identification & locations
Identify it by interlocking visible grains, abundant light feldspar/quartz, and scattered dark minerals; it should not fizz with dilute acid and should scratch glass. Value is typically $1–$10 as a common loose specimen, or roughly $10–$30 if unusually attractive and polished.
