metamorphic
Gneiss
Banded Metamorphic Rock (Gneiss)
Hardness: 6-7 on Mohs scale. Color: Grey with pinkish-red and dark mineral banding. Luster: Dull to slightly vitreous. Structure: Medium to coarse-grained metamorphic texture showing distinctive gneissic foliation/banding.
- Hardness
- 6-7 on Mohs scale
- Color
- Grey with pinkish-red and dark mineral banding
- Luster
- Dull to slightly vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Grey with pinkish-red and dark mineral banding. Luster: Dull to slightly vitreous. Structure: Medium to coarse-grained metamorphic texture showing distinctive gneissic foliation/banding.
Formation & geological history
Formed under high-grade regional metamorphism (high temperatures and high pressure) from igneous rocks like granite or sedimentary rocks like shale. Typically associated with pre-Cambrian shield areas and mountain-building regions.
Uses & applications
Widely used as crushed stone for road construction, aggregate, landscaping stone, dimension stone for building facades, and decorative garden rock.
Geological facts
Gneiss is one of the oldest rock types found on Earth. The Acasta Gneiss in Northwest Territories, Canada, is dated at nearly 4.0 billion years old, making it one of the oldest known intact crustal rocks on the planet.
Field identification & locations
Identified in the field by its distinct alternating light and dark mineral bands (gneissic banding) and granular texture without easy cleavage. Commonly found in exposed Canadian Shield regions, Appalachian and Rocky Mountains, and Scandinavia.
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