metamorphic
Gneiss
Gneiss (High-grade metamorphic rock)
Hardness: 6-7 (Mohs scale); Color: Gray, pink, white with characteristic banding; Luster: Dull to vitreous; Structure: Foliated with distinct compositional banding (gneissose banding); Gravity: 2.6-2.9
- Hardness
- 6-7 (Mohs scale)
- Color
- Gray, pink, white with characteristic banding
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Gray, pink, white with characteristic banding; Luster: Dull to vitreous; Structure: Foliated with distinct compositional banding (gneissose banding); Gravity: 2.6-2.9
Formation & geological history
Formed by high-grade regional metamorphism of igneous (granite) or sedimentary rocks (shale) under intense heat and pressure, often found in the cores of mountain ranges and ancient continental shields.
Uses & applications
Commonly used as a dimension stone for flooring, wall facing, and grave markers; also used as crushed stone in road construction and landscaping.
Geological facts
Gneiss is among the oldest known rocks on Earth; the Acasta Gneiss in Canada is approximately 4.03 billion years old. The term comes from the Middle High German verb 'gneist' meaning 'to spark' because the rock glitters.
Field identification & locations
Identify by looking for 'gneissose banding'—distinct light and dark layers of minerals like quartz, feldspar, and mica. It is found in deep metamorphic terrains like the Appalachian or Himalayan mountains.
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