metamorphic
Gneiss
Gneiss
Hardness: 6-7; Color: Gray, pink, white, and black; Luster: Dull to vitreous; Structure: Foliated with distinct mineral banding; Specific Gravity: 2.6-2.9
- Hardness
- 6-7
- Color
- Gray, pink, white, and black
- Luster
- Dull to vitreous
Identified More metamorphic →
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Physical properties
Hardness: 6-7; Color: Gray, pink, white, and black; Luster: Dull to vitreous; Structure: Foliated with distinct mineral banding; Specific Gravity: 2.6-2.9
Formation & geological history
Formed through high-grade regional metamorphism of igneous (granite) or sedimentary (shale) protoliths under intense heat and pressure deep within the Earth's crust.
Uses & applications
Used as a dimension stone for flooring, facades, and Gravestones; also crushed for use as road aggregate and railroad ballast.
Geological facts
The Acasta Gneiss in Canada is one of the oldest known intact crustal rocks on Earth, dated at approximately 4.03 billion years old.
Field identification & locations
Identify by looking for 'gneissose banding'—distinct light and dark layers of alternating minerals like quartz and mica. Commonly found in the cores of mountain ranges.
