metamorphic
Gneiss
Gneiss
Hardness (Mohs): 6-7; Color: Banded grey, white, and black; Luster: Dull to vitreous; Structure: Foliated with distinct bands (gneissose banding); Specific Gravity: 2.6-2.9
- Color
- Banded grey, white, and black
- Luster
- Dull to vitreous
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Physical properties
Hardness (Mohs): 6-7; Color: Banded grey, white, and black; Luster: Dull to vitreous; Structure: Foliated with distinct bands (gneissose banding); Specific Gravity: 2.6-2.9
Formation & geological history
Formed through high-grade regional metamorphism of igneous or sedimentary rocks (protoliths) under intense heat and pressure deep in the Earth's crust.
Uses & applications
Used in construction as crushed stone, dimension stone for flooring and facades, and as landscaping material. Fine specimens are used for educational collections.
Geological facts
Gneiss is one of the oldest known rock types on Earth, with some specimens in the Acasta Gneiss complex dating back over 4 billion years.
Field identification & locations
Identify in the field by looking for distinct light and dark mineral banding (foliation). Common in core regions of mountain ranges and ancient continental shields.
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