igneous
Granite or granitic gneiss glacial erratic
Biotite granite; chiefly quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse, speckled gray rock with visible pale feldspar/quartz and dark mica; quartz hardness 7, feldspar 6, overall Mohs ~6–7. Nonmetallic luster, interlocking crystalline texture, massive with poor cleavage as a whole; rounded surface reflects weathering and transport.
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Physical properties
Coarse, speckled gray rock with visible pale feldspar/quartz and dark mica; quartz hardness 7, feldspar 6, overall Mohs ~6–7. Nonmetallic luster, interlocking crystalline texture, massive with poor cleavage as a whole; rounded surface reflects weathering and transport.
Formation & geological history
Most likely an ice-rounded glacial erratic formed by slow crystallization of magma deep in the crust, commonly Precambrian to Paleozoic in age. Its smooth shape may result from glacial abrasion and later stream or soil weathering.
Uses & applications
Commonly used as building stone, aggregate, curbing, landscaping boulders, and monuments; this ordinary outdoor specimen has little jewelry or collector value.
Geological facts
The image does not clearly show foliation, so granite is more likely than gneiss, though field inspection may reveal faint banding. The rounded form is not the original igneous shape but a transport-weathering feature.
Field identification & locations
Look for interlocking light quartz/feldspar grains, scattered black biotite, and no vesicles or sedimentary layers; a hand lens and fresh broken surface improve identification. Common worldwide, especially in glaciated regions such as Canada, New England, Scandinavia, and the northern Midwest.
