igneous
Weathered granite or granitic gneiss
Granite; mainly quartz, alkali feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, pinkish-tan and gray, with visible interlocking crystals and rusty iron-oxide staining; quartz is Mohs 7, feldspar about 6, with vitreous to dull luster. The specimen appears massive and lacks obvious cleavage as a whole, though feldspar grains cleave.
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Physical properties
Coarse-grained, pinkish-tan and gray, with visible interlocking crystals and rusty iron-oxide staining; quartz is Mohs 7, feldspar about 6, with vitreous to dull luster. The specimen appears massive and lacks obvious cleavage as a whole, though feldspar grains cleave.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the continental crust, commonly during Precambrian to Mesozoic plutonic events; surface weathering produced the orange-brown staining. If foliation is present, it may instead be granitic gneiss formed by high-grade metamorphism.
Uses & applications
Used as dimension stone, countertops, monuments, aggregate, and landscaping rock; attractive pieces may be collected but this fragment has little gem value.
Geological facts
Granite’s coarse texture records slow underground cooling, allowing large crystals to grow. Iron oxidation commonly creates the rusty orange coating seen here.
Field identification & locations
Look for interlocking pink/white feldspar, glassy gray quartz, and black mica; a hand lens and streak/acid tests help distinguish it from sandstone. Common worldwide in continental shields and mountain belts.
