igneous
Quartz-bearing granite or granitic gneiss
Granite; primarily quartz (SiO₂), feldspar, and mica, possibly weakly metamorphosed
AI-generated identification · may be incorrectCoarse-grained, irregular interlocking crystals with pale gray/white quartz-feldspar and dark mica or amphibole; vitreous quartz and blocky feldspar are likely. Estimated Mohs hardness 6–7; no obvious cleavage on the broken surface; typical specific gravity 2.6–2.8.
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Physical properties
Coarse-grained, irregular interlocking crystals with pale gray/white quartz-feldspar and dark mica or amphibole; vitreous quartz and blocky feldspar are likely. Estimated Mohs hardness 6–7; no obvious cleavage on the broken surface; typical specific gravity 2.6–2.8.
Formation & geological history
Formed by slow cooling of silica-rich magma deep underground, likely Precambrian in age if collected near northeastern Minnesota. The rough shape appears naturally broken or weathered.
Uses & applications
Commonly used as crushed stone, aggregate, building stone, countertops, and decorative material; this small, weathered piece has little commercial value.
Geological facts
The greenish-gray and brown colors may reflect chlorite, weathering, or iron staining. The regional setting near 46.7°N, 92.0°W strongly favors Precambrian granitic rocks and gneisses of the Lake Superior region.
Field identification & locations
Look for visible quartz, feldspar, and dark mica grains; granite is generally massive, while gneiss shows distinct mineral banding. A glassy quartz grain scratches glass, whereas feldspar commonly shows two cleavage directions; confirmation requires a fresh surface and hand lens.
