metamorphic
Banded Gneiss
Gneiss (Metamorphic Rock)
Hardness: 6-7 on Mohs scale; Color: Gray, black, and tan banding; Luster: Dull to slightly silky; Crystal structure: Coarse-grained with foliation; Specific Gravity: 2.6-2.9
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, black, and tan banding
- Luster
- Dull to slightly silky
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray, black, and tan banding; Luster: Dull to slightly silky; Crystal structure: Coarse-grained with foliation; Specific Gravity: 2.6-2.9
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under extreme heat and pressure, typically during mountain-building events. These rocks can be billions of years old.
Uses & applications
Used as building stone, decorative landscaping, crushed stone for construction, and occasionally for lapidary work if highly attractive.
Geological facts
Gneiss is some of the oldest rock found on Earth, with some specimens from the Acasta Gneiss complex dating back over 4 billion years.
Field identification & locations
Identify by its distinct light and dark alternating bands (gneissose banding) and coarse grain size. It is common in the cores of mountain ranges and stable continental shields.
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