metamorphic
Feldspathic gneiss (likely augen gneiss)
Quartz–feldspar–mica gneiss; commonly dominated by quartz, K-feldspar/plagioclase, and biotite
AI-generated identification · may be incorrectCoarse-grained, strongly foliated rock with pale pink feldspar, gray quartz, and dark mica/amphibole bands; vitreous quartz luster and feldspar cleavage. Typical hardness is about 6–7 Mohs, with no single crystal structure because it is a polymineralic rock.
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Physical properties
Coarse-grained, strongly foliated rock with pale pink feldspar, gray quartz, and dark mica/amphibole bands; vitreous quartz luster and feldspar cleavage. Typical hardness is about 6–7 Mohs, with no single crystal structure because it is a polymineralic rock.
Formation & geological history
Formed when granitic or volcanic protoliths underwent high-grade regional metamorphism, producing compositional banding and stretched feldspar “eyes.” Such rocks commonly formed during Precambrian to Paleozoic mountain-building events.
Uses & applications
Used as crushed stone, dimension stone, landscaping rock, and occasionally as decorative slabs; attractive pieces are collected but generally have modest value.
Geological facts
The irregular light-colored patches and streaks are characteristic of gneissic segregation and deformation, distinguishing it from uniformly crystalline granite.
Field identification & locations
Identify it by alternating light and dark mineral bands, coarse grains, and a fractured rather than uniformly granular texture; common in ancient continental shields and mountain belts worldwide. The photograph alone cannot confirm exact subtype.
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