metamorphic
Gneiss
Gneissic Metamorphic Rock
Hardness: 6-7 on Mohs scale. Color: Gray, white, or pink with darker streaks. Luster: Dull to pearly. Structure: Foliated with distinct mineral banding (gneissic banding). Components: Quartz, feldspar, and darker mica or amphibole.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, white, or pink with darker streaks
- Luster
- Dull to pearly
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Gray, white, or pink with darker streaks. Luster: Dull to pearly. Structure: Foliated with distinct mineral banding (gneissic banding). Components: Quartz, feldspar, and darker mica or amphibole.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and pressure. Often represents some of the oldest crustal material on Earth.
Uses & applications
Commonly used as a decorative crushed stone in construction, road base, and as facing stones for buildings and landscaping.
Geological facts
The Acasta Gneiss in Canada is one of the oldest known rock formations on Earth, dated to approximately 4 billion years ago.
Field identification & locations
Identify in the field by looking for 'salt and pepper' appearance with distinct parallel bands or layers of different colors. It is commonly found in the roots of mountain ranges and glacial deposits.
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