metamorphic
Biotite-bearing granitic gneiss
Quartz–feldspar–biotite gneiss; composition approximately quartz + plagioclase/K-feldspar + biotite ± amphibole
AI-generated identification · may be incorrectCoarse, speckled gray-pink rock with dark flaky biotite and pale quartz/feldspar; weak foliation and irregular banding are visible. Hardness is roughly 6–7 overall, with vitreous quartz, nonmetallic luster, and feldspar cleavage; density is about 2.6–2.8 g/cm³.
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Physical properties
Coarse, speckled gray-pink rock with dark flaky biotite and pale quartz/feldspar; weak foliation and irregular banding are visible. Hardness is roughly 6–7 overall, with vitreous quartz, nonmetallic luster, and feldspar cleavage; density is about 2.6–2.8 g/cm³.
Formation & geological history
Likely metamorphosed granitic rock formed during Precambrian–Paleozoic mountain-building, under high temperature and pressure. The Québec City region commonly exposes Grenville or Appalachian crystalline rocks, making this identification geologically plausible, though the exact locality cannot be determined from the photo.
Uses & applications
Used as crushed stone, aggregate, building stone, and occasionally decorative dimension stone; attractive pieces are collected but usually have modest value.
Geological facts
The dark minerals are probably biotite mica, whose thin flakes split into flexible sheets. Pink areas are potassium feldspar, gray translucent grains are quartz, and white grains are commonly plagioclase.
Field identification & locations
Look for coarse interlocking grains, mica flakes, quartz, and feldspar rather than sedimentary layering. A fresh surface, streak, magnetism test, and thin-section examination would distinguish it from granite or amphibolite more confidently.
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