igneous
Biotite-bearing granite (possibly granitic gneiss)
Granite: quartz + potassium feldspar + plagioclase + biotite; approximate silica-rich granitoid
AI-generated identification · may be incorrectCoarse, speckled tan-gray rock with dark biotite/hornblende and light feldspar/quartz; granular texture, generally vitreous-to-dull luster, no obvious cleavage as a whole, Mohs hardness about 6–7, specific gravity roughly 2.63–2.75. Subtle alignment or banding could indicate gneiss rather than granite.
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Physical properties
Coarse, speckled tan-gray rock with dark biotite/hornblende and light feldspar/quartz; granular texture, generally vitreous-to-dull luster, no obvious cleavage as a whole, Mohs hardness about 6–7, specific gravity roughly 2.63–2.75. Subtle alignment or banding could indicate gneiss rather than granite.
Formation & geological history
Slow crystallization of silica-rich magma deep in the crust, typically Precambrian to Paleozoic in age; if metamorphic banding is confirmed, it formed by high-grade deformation and recrystallization. This composition is plausible around Québec’s Grenville and related crystalline terranes.
Uses & applications
Widely used as dimension stone, countertops, monuments, aggregate, and landscaping rock; attractive polished pieces have modest decorative or collector value.
Geological facts
Quartz is typically gray or glassy, feldspar cream to pink, and biotite forms black flaky grains. Weathering commonly produces the rusty-brown surface visible here.
Field identification & locations
Identify with a hand lens by interlocking quartz and feldspar grains plus black mica; a steel file should barely scratch it, while glass can scratch it. Common across Québec and much of the Canadian Shield; inspect a fresh broken surface for clearer mineral colors and any gneissic banding.
