metamorphic
Gneiss with Quartz/Feldspar Vein
Felsic to intermediate gneiss
Hardness: 6-7 on Mohs scale. Color: Pale pinkish-tan background with dark green/grey ferromagnesian mineral bands and white/translucent quartz grains. Luster: Dull to vitreous. Structure: Foliated with distinct compositional banding.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Pale pinkish-tan background with dark green/grey ferromagnesian mineral bands and white/translucent quartz grains. Luster: Dull to vitreous. Structure: Foliated with distinct compositional banding.
Formation & geological history
Formed under high-temperature and high-pressure regional metamorphism deep within the Earth's crust, causing minerals to recrystallize and segregate into visible light and dark bands.
Uses & applications
Widely used as crushed stone for construction, aggregate in concrete and asphalt, dimension stone for countertops and building facades, and landscape decoration.
Geological facts
Gneiss is one of the oldest rock types found on Earth, with some specimens like the Acasta Gneiss in Canada dating back nearly 4 billion years. The distinct banding distinguishes it from unfoliated rocks like granite.
Field identification & locations
Identified in the field by its distinct alternating dark and light mineral bands (foliation) and coarse crystalline texture. Commonly found in continental shield areas and mountain belts worldwide.
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