igneous
Glacial granite/granitoid boulder
Granite to granodiorite; chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, light gray, massive, and weakly speckled with dark minerals; vitreous quartz and feldspar give a granular texture. Typical hardness is about 6–7 Mohs, with no obvious cleavage as a whole rock and specific gravity around 2.6–2.7.
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Physical properties
Coarse-grained, light gray, massive, and weakly speckled with dark minerals; vitreous quartz and feldspar give a granular texture. Typical hardness is about 6–7 Mohs, with no obvious cleavage as a whole rock and specific gravity around 2.6–2.7.
Formation & geological history
An intrusive igneous rock that crystallized slowly deep underground, probably hundreds of millions to over a billion years ago. The rounded shape and surface weathering strongly suggest transport and abrasion by Pleistocene glacial ice or meltwater.
Uses & applications
Commonly used as crushed stone, aggregate, building stone, curbing, monuments, and landscaping rock; usually has little individual collector value.
Geological facts
The location near 40.1°N, 85.4°W in east-central Indiana is dominated by glacial and sedimentary deposits, so this is likely an erratic transported from Canadian or northern Great Lakes source rocks rather than locally formed bedrock.
Field identification & locations
Identify it by visible interlocking quartz-feldspar grains, scattered dark mica/amphibole, gray color, and a rounded glacial form. A hand lens, streak test, and acid test can help distinguish it from quartzite or metamorphic gneiss; the faint linear band may be a weathering seam or compositional variation.
