metamorphic
Banded Gneiss with Quartz Veining
Gneiss (High-grade Regional Metamorphism)
Hardness: 6-7 (Mohs scale), Color: Alternating bands of dark grey/black and white/cream, Luster: Vitreous to dull, Crystal Structure: Coarse-grained foliated, Cleavage: None (poorly defined foliation)
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Alternating bands of dark grey/black and white/cream, Luster: Vitreous to dull, Crystal Structure: Coarse-grained foliated, Cleavage: None (poorly defined foliation)
Formation & geological history
Formed under extreme temperature and pressure deep within the Earth's crust, often during mountain-building events (orogeny). The quartz veins likely formed later from hydrothermal fluids filling fractures.
Uses & applications
Used as dimension stone in construction (flooring, facing), decorative landscaping, and as crushed stone for road aggregate.
Geological facts
Gneiss is among the oldest types of rock on Earth, with some specimens like the Acasta Gneiss dating back over 4 billion years.
Field identification & locations
Identify by distinct colored bands (gneissic banding) and granular texture. Common in continental shields and core of mountain ranges. To identify, look for alternating layers of minerals like quartz, feldspar, and mica.
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