metamorphic
Gneiss
Gneiss
Hardness: 6-7 (Mohs scale), Color: Banded grey, white, black, and tan. Luster: Dull to vitreous. Crystal Structure: Coarse-grained foliated texture. Specific Gravity: 2.6-3.0.
- Hardness
- 6-7 (Mohs scale), Color: Banded grey, white, black, and tan
- Color
- Banded grey, white, black, and tan
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Banded grey, white, black, and tan. Luster: Dull to vitreous. Crystal Structure: Coarse-grained foliated texture. Specific Gravity: 2.6-3.0.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks (like granite or shale) under extreme heat and pressure, often found in the roots of mountain ranges.
Uses & applications
Used as a decorative stone in architecture, flooring, paving, and crushed stone for road construction and landscaping.
Geological facts
Gneiss is some of the oldest rock found on Earth’s surface; the Acasta Gneiss in Canada is approximately 4.03 billion years old. The 'gneissic banding' is caused by the segregation of light and dark minerals.
Field identification & locations
Identify in the field by looking for distinct layers or 'bands' of light quartz/feldspar and dark biotite/amphibole. It does not split easily along planes like schist. Common in continental shields.
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