metamorphic
Granite Gneiss
Gneiss (High-grade regional metamorphic rock)
Hardness: 6-7 on Mohs scale; Color: Pinkish-brown with dark bands; Luster: Dull to sub-vitreous; Crystal Structure: Foliated with visible mineral 'banding'; Specific Gravity: 2.6-2.9
- Hardness
- 6-7 on Mohs scale
- Color
- Pinkish-brown with dark bands
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Pinkish-brown with dark bands; Luster: Dull to sub-vitreous; Crystal Structure: Foliated with visible mineral 'banding'; Specific Gravity: 2.6-2.9
Formation & geological history
Formed through high-pressure, high-temperature regional metamorphism of igneous granite or sedimentary protoliths. It originates deep within the Earth's crust at convergent plate boundaries.
Uses & applications
Used for construction, paving stones, architectural facades, and occasionally as decorative gravel or landscaping stone.
Geological facts
Gneiss is some of the oldest rock found on Earth, with the Acasta Gneiss in Canada dating back over 4 billion years. The distinct banding is called 'gneissic banding'.
Field identification & locations
Identified by coarse mineral grains arranged in alternating light and dark layers. Common in mountainous regions with exposed continental shields. Look for a 'salty and pepper' or striped appearance.
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