metamorphic
Gneiss
Metamorphic Foliated Gneiss
Hardness: 6-7 on Mohs scale. Color: Grey, tan, brown, white, and black banded layers. Luster: Dull to vitreous. Structure: Foliated with distinct compositional banding (gneissic banding).
- Hardness
- 6-7 on Mohs scale
- Color
- Grey, tan, brown, white, and black banded layers
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Grey, tan, brown, white, and black banded layers. Luster: Dull to vitreous. Structure: Foliated with distinct compositional banding (gneissic banding).
Formation & geological history
Formed under high-grade regional metamorphism involving intense heat and pressure acting on pre-existing igneous or sedimentary rocks like granite or shale.
Uses & applications
Used as crushed stone in construction, dimension stone for buildings and landscaping, and as decorative gravel.
Geological facts
The distinct light and dark bands in gneiss are caused by the segregation of light minerals (quartz, feldspar) and dark minerals (biotite, amphibole) under high thermal pressure.
Field identification & locations
Identified by visible alternating light and dark mineral bands. Found worldwide in ancient shield regions and mountain belts.
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