igneous
Weathered granite or granitic gneiss cobble
Granite; chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectCoarse granular, tan-gray rock with dark mica or amphibole; typically Mohs 6–7, dull to subtly glassy luster, interlocking crystals, and no cleavage as a whole. The rounded shape and dark weathering rind indicate natural abrasion and surface alteration.
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Physical properties
Coarse granular, tan-gray rock with dark mica or amphibole; typically Mohs 6–7, dull to subtly glassy luster, interlocking crystals, and no cleavage as a whole. The rounded shape and dark weathering rind indicate natural abrasion and surface alteration.
Formation & geological history
Formed by slow cooling of silica-rich magma deep in the continental crust, commonly during Precambrian to Phanerozoic mountain-building events; later exposed and rounded in stream or glacial environments.
Uses & applications
Crushed granite is used for aggregate, road base, and construction stone; attractive pieces may be used as landscaping or teaching specimens, but this small cobble has little commercial value.
Geological facts
Granite commonly shows visible quartz and feldspar grains, while gneiss displays compositional banding; the image is not detailed enough to distinguish them confidently.
Field identification & locations
Look for interlocking light feldspar/quartz grains with scattered black mica or amphibole; a streak test is generally white, and the rock does not fizz with dilute acid. Common worldwide, especially in exposed continental shield and mountain regions.
