metamorphic
Granite Gneiss
Gneiss (High-grade Metamorphic Rock)
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (gray, white, pink, black); Luster: Vitreous to dull; Crystal structure: Planar arrangement of minerals (foliation) with visible banding; Specific gravity: 2.6-2.9
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (gray, white, pink, black)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (gray, white, pink, black); Luster: Vitreous to dull; Crystal structure: Planar arrangement of minerals (foliation) with visible banding; Specific gravity: 2.6-2.9
Formation & geological history
Formed from the high-pressure and high-temperature metamorphism of igneous granite or sedimentary protoliths. The provided coordinates (Kola Peninsula, Russia) are in the Baltic Shield, an area dominated by Precambrian crystalline basement rocks often over 2.5 billion years old.
Uses & applications
Used widely in construction as crushed stone for road bases, or if large enough, as ornamental building stone, countertops, and flooring. Highly durable and resistant to erosion.
Geological facts
Gneiss is one of the oldest rock types on Earth. The Acasta Gneiss in Canada is the oldest known crustal rock at 4 billion years. In the Kola region, these rocks are part of the Murmansk Block and represent some of the most stable parts of the Earth's crust.
Field identification & locations
Identify by 'gneissic banding', where minerals like quartz, feldspar, and mica segregate into distinct light and dark layers. Common across the Murmansk region. In the field, look for sparkling mica and the characteristic banded texture.
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