metamorphic
Granite Gneiss
Gneiss (containing quartz, alkali feldspar, plagioclase, biotite/amphibole)
Hardness: 6-7 on Mohs scale. Color: Speckled pink, white, gray, and dark green/black with distinct foliation or banding. Luster: Vitreous to dull. Texture: Medium to coarse-grained, crystalline.
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Speckled pink, white, gray, and dark green/black with distinct foliation or banding. Luster: Vitreous to dull. Texture: Medium to coarse-grained, crystalline.
Formation & geological history
Formed through high-grade regional metamorphism of igneous granite or sedimentary rocks under extreme pressure and high temperature deep within continental crust.
Uses & applications
Used widely as crushed stone for construction, aggregate, road base, dimension stone, landscaping, and decorative rock specimens.
Geological facts
Gneiss often shows prominent alternating light and dark mineral bands known as gneissic banding, which forms as minerals recrystallize and segregate under directional pressure.
Field identification & locations
Identify in the field by its distinct banded texture, hardness, and visible interlocking grains of pink feldspar, clear-gray quartz, and dark mica or hornblende. Commonly found in shield regions and ancient mountain cores worldwide.
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