Gneiss
Rock made of feldspar, quartz, mica
Common
A coarse, high-grade metamorphic rock striped in light and dark bands. Some of the oldest rocks on Earth are gneisses, such as the Acasta Gneiss of northern Canada.
Rock
- Kind of rock
- Metamorphic rock
- Rock family
- Schist and gneiss
- Texture
- banded, foliated (splits along its layers)
- Also contains
- Garnet
- How it forms
- Igneous or sedimentary rock at pressures of 2 to 15 kilobars and above 300 °C separates into bands without melting.
- Uses
- Building stone, as the facoidal gneiss of Rio de Janeiro, and road aggregate.
Crystallography
- Habits
- Foliated, Granular
Physical properties
- Luster
- Vitreous
- Colors
- gray, pink, white, black
- Transparency
- Opaque
Geology
- Origins
- Metamorphic
- Geography
- worldwide, Canada (Acasta Gneiss), Scotland (Lewisian gneiss), Brazil (Rio de Janeiro)
Classification
- Rarity
- Common
- Gem quality
- No
Sources
- Gneiss. Wikipedia.
- S. Robertson, BGS Rock Classification Scheme, Volume 2: Classification of metamorphic rocks (Research Report RR 99-02). British Geological Survey, 1999.
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