metamorphic
Gneiss
Metamorphic Gneiss
Hardness: 6-7 on Mohs scale; Color: reddish-brown with whitish speckling and banding; Luster: earthy to dull with slight vitreous sparkle from quartz/feldspar; Cleavage: poor/irregular fracture; Specific Gravity: 2.6 - 2.9
- Hardness
- 6-7 on Mohs scale
- Color
- reddish-brown with whitish speckling and banding
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Physical properties
Hardness: 6-7 on Mohs scale; Color: reddish-brown with whitish speckling and banding; Luster: earthy to dull with slight vitreous sparkle from quartz/feldspar; Cleavage: poor/irregular fracture; Specific Gravity: 2.6 - 2.9
Formation & geological history
Formed through high-grade regional metamorphism of igneous (like granite) or sedimentary rocks under extreme heat and pressure deep within Earth's crust.
Uses & applications
Used in construction as crushed stone, dimension stone for buildings and countertops, landscape rock, and educational geological specimens.
Geological facts
Gneissic banding is a distinct texture where light-colored quartz and feldspar alternate with dark-colored amphibole or mica minerals due to directional stress during metamorphic processes.
Field identification & locations
Identified by distinct light and dark mineral segregation (gneissic foliation) and crystalline coarse-grained texture. Extremely common in ancient shield areas worldwide like North America and Scandinavia.
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