metamorphic
Banded Gneiss
Gneiss (Metamorphic rock predominantly containing quartz, feldspar, and mica)
Hardness: 6-7 on Mohs scale; Color: Gray, black, and white bands; Luster: Dull to slightly pearly; Crystal structure: Coarse-grained foliated texture with distinct alternating layers of light and dark minerals.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, black, and white bands
- Luster
- Dull to slightly pearly
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray, black, and white bands; Luster: Dull to slightly pearly; Crystal structure: Coarse-grained foliated texture with distinct alternating layers of light and dark minerals.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks at extreme temperatures and pressures deep within the Earth's crust, often during mountain-building events.
Uses & applications
Used primarily as a decorative stone in landscaping, aquarium decor, and sometimes as crushed stone for road construction or high-end building veneer.
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 banding is caused by the segregation of minerals during intense pressure.
Field identification & locations
Identify by looking for 'gneissose banding' consisting of alternating light (quartz/feldspar) and dark (biotite/amphibole) mineral layers. Commonly found in glaciated riverbeds or mountain ranges.
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