igneous
Weathered granitic rock fragment
Granitoid, likely granite or granodiorite; predominantly quartz, feldspar, and mica
AI-generated identification · may be incorrectHardness about 6–7 Mohs; coarse, speckled gray-brown appearance with dull to faintly glassy luster. Interlocking crystalline texture and irregular fracture; exact mineral proportions are unclear from the image.
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Physical properties
Hardness about 6–7 Mohs; coarse, speckled gray-brown appearance with dull to faintly glassy luster. Interlocking crystalline texture and irregular fracture; exact mineral proportions are unclear from the image.
Formation & geological history
Formed when silica-rich magma slowly cooled deep underground, producing coarse crystals, then weathered and eroded into a fragment. Granitoids commonly formed during Precambrian to younger continental mountain-building events.
Uses & applications
Used as aggregate, building stone, curbing, and landscaping material; small specimens have minimal collector value unless unusually attractive or locality-labeled.
Geological facts
The rusty brown surface likely reflects oxidation of iron-bearing biotite or other minerals. A fresh broken surface should reveal lighter gray feldspar and translucent quartz grains.
Field identification & locations
Common in continental crust and found widely in places such as the Sierra Nevada, Canadian Shield, Appalachians, and many gravel deposits. Identify by visible interlocking quartz, feldspar, and dark mica; acid testing is generally unnecessary.
