metamorphic
Banded Gneiss
Gneiss (Metamorphic high-grade rock)
Hardness (Mohs scale): 6-7. Color: Alternating light (pink/tan) and dark (grey/black) bands. Luster: Dull to pearly. Texture: Coarse-grained with distinct foliation (gneissic banding). Specific gravity: 2.6-2.9.
- Color
- Alternating light (pink/tan) and dark (grey/black) bands
- Luster
- Dull to pearly
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Physical properties
Hardness (Mohs scale): 6-7. Color: Alternating light (pink/tan) and dark (grey/black) bands. Luster: Dull to pearly. Texture: Coarse-grained with distinct foliation (gneissic banding). Specific gravity: 2.6-2.9.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks at extreme temperatures and pressures. This specimen is a water-worn river stone, smoothed over thousands of years.
Uses & applications
Used as a decorative stone, in construction (crushed stone), as building veneers, and as a durable material for countertops or landscaping.
Geological facts
The Acasta Gneiss is one of the oldest known crustal rock outcrops on Earth, dating back approximately 4 billion years. The distinct bands are caused by the separation of minerals like quartz/feldspar and biotite/amphibole under pressure.
Field identification & locations
Identify in the field by looking for 'zebra-like' stripes or bands of different colors. Commonly found in mountainous regions or glacial deposits like the Great Lakes region and Canadian Shield.
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