metamorphic

Weathered granitic gneiss

Felsic orthogneiss; chiefly quartz, feldspar, and mica

AI-generated identification · may be incorrect

Coarse, strongly foliated and folded rock with tan-gray quartz/feldspar-rich bands and dark biotite-rich streaks; hardness about 6–7 Mohs, vitreous to dull luster, irregular fracture, and no obvious cleavage as a whole.

Identified September 18, 2026More metamorphic →

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Physical properties

Formation & geological history

Originally formed as granite, then recrystallized and intensely deformed during high-grade regional metamorphism, commonly during Precambrian or Paleozoic mountain building. Exact age and identification require a fresh surface or laboratory analysis.

Uses & applications

Used locally as landscaping stone, riprap, building stone, and decorative facing; attractive polished pieces may be collected, but this boulder has limited commercial value.

Geological facts

The swirling texture reflects ductile deformation under great heat and pressure, while surface browning results from weathering of iron-bearing minerals.

Field identification & locations

Identify it by coarse interlocking crystals, alternating light and dark mineral bands, and foliation; distinguish it from unfoliated granite by its streaked, folded fabric. Common in ancient continental shields and metamorphic mountain belts.