metamorphic

Dark schist or gneiss cobble

Foliated metamorphic rock, likely biotite–quartz–feldspar schist/gneiss

AI-generated identification · may be incorrect

Gray-brown, fine- to medium-grained, with abundant reflective mica flakes and a weakly foliated texture; likely Mohs 2–7 depending on the exposed mineral, with vitreous to pearly luster. Cleavage is mainly within mica; density is approximately 2.7–2.9 g/cm³.

Identified September 6, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or a granitic protolith was subjected to elevated pressure and temperature, producing mica-rich foliation. Glacial transport and abrasion likely rounded this specimen; such rocks are common in the Precambrian Canadian Shield and nearby glacial deposits.

Uses & applications

Commonly used as crushed aggregate, landscaping stone, and occasionally decorative building stone. This small rounded piece has little commercial value but may be useful as a teaching or collection specimen.

Geological facts

The glitter is probably biotite or muscovite mica rather than metallic ore. The Montreal-area region near 45.5°N, 73.6°W contains abundant glacially transported metamorphic rocks from the Laurentian/Canadian Shield.

Field identification & locations

Look for planar mineral alignment, mica that separates into thin flakes, and hard gray quartz/feldspar grains. A streak test, magnet test, and close inspection of foliation would distinguish it from dark granite or mica-rich volcanic rock; the image does not support a precise species identification.