metamorphic
Gneiss
Gneiss
Hardness: 6-7 on Mohs scale; Color: Gray, pink, or brownish with distinct light and dark banding; Luster: Dull to vitreous; Structure: Foliated with coarse mineral grains; Cleavage: Poorly defined.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, pink, or brownish with distinct light and dark banding
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray, pink, or brownish with distinct light and dark banding; Luster: Dull to vitreous; Structure: Foliated with coarse mineral grains; Cleavage: Poorly defined.
Formation & geological history
Formed by high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and pressure. Often billions of years old, forming the roots of mountain ranges.
Uses & applications
Used as a dimension stone for flooring, gravestones, and facing on buildings; also used as crushed stone for road construction and landscaping.
Geological facts
Gneiss is one of the oldest rock types on Earth, with some specimens like the Acasta Gneiss dating back over 4 billion years. The name comes from a German word meaning 'sparkling'.
Field identification & locations
Identified by 'gneissose banding' (segregation of light and dark minerals). Commonly found in the cores of mountain belts and Precambrian shield areas like the Canadian Shield.
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