metamorphic
Banded Gneiss
Gneiss (High-grade Regional Metamorphic Rock)
Hardness: 6-7 on Mohs scale. Color: Alternating light (quartz/feldspar) and dark (biotite/amphibole) bands. Luster: Dull to vitreous. Structure: Gneissic banding (foliated). Cleavage: Poor.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Alternating light (quartz/feldspar) and dark (biotite/amphibole) bands. Luster: Dull to vitreous. Structure: Gneissic banding (foliated). Cleavage: Poor.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and pressure, typically deep within tectonic plate boundaries.
Uses & applications
Used as a decorative stone in landscaping, crushed stone for construction, dimension stone for flooring and countertops, and for geological education.
Geological facts
Gneiss is some of the oldest rock on Earth, with the Acasta Gneiss in Canada dating back over 4 billion years. The distinct banding is caused by the segregation of minerals during metamorphism.
Field identification & locations
Identify in the field by looking for distinct layers or bands of different mineral compositions. Found globally in the roots of mountain ranges and ancient continental shields.
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