metamorphic
Gneiss
Gneiss
Hardness: 6-7 on Mohs scale; Color: Varies with mineral composition, commonly banded light and dark grey, pink, or green; Luster: Vitreous to dull; Crystal structure: Foliated, banded texture with distinct alternating light and dark mineral bands; Specific gravity: 2.6-3.0
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Varies with mineral composition, commonly banded light and dark grey, pink, or green; Luster: Vitreous to dull; Crystal structure: Foliated, banded texture with distinct alternating light and dark mineral bands; Specific gravity: 2.6-3.0
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks (such as granite or shale) under extreme heat and pressure deep within the Earth's crust, typically dating from the Precambrian to Cenozoic eras.
Uses & applications
Used primarily as dimension stone in construction, building facades, flooring, landscaping, and occasionally as decorative aggregate.
Geological facts
Gneiss contains some of the oldest known rocks on Earth, with certain formations dating back over 4 billion years.
Field identification & locations
Easily identified by its distinct alternating light (quartz and feldspar) and dark (biotite and amphibole) compositional banding, known as gneissic banding. Found worldwide in ancient shield areas and mountain belts.
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