metamorphic
Gneiss
Gneiss
Hardness: 6-7 on Mohs scale. Color: Varies widely, often banded with alternating light (quartz, feldspar) and dark (biotite, amphibole) minerals. Luster: Vitreous to dull. Crystal structure: Foliated, coarse-grained. Cleavage: Poor. Specific gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Varies widely, often banded with alternating light (quartz, feldspar) and dark (biotite, amphibole) minerals. Luster: Vitreous to dull. Crystal structure: Foliated, coarse-grained. Cleavage: Poor. Specific gravity: 2.6-2.9.
Formation & geological history
Formed by high-grade regional metamorphism, altering pre-existing rocks such as granite or sedimentary rocks under extreme heat and pressure deep within the Earth's crust.
Uses & applications
Commonly used in construction, as dimension stone for buildings, flooring, facing stone, and aggregates for road construction.
Geological facts
Gneiss contains some of the oldest rocks found on Earth, with certain formations dating back over 4 billion years.
Field identification & locations
Easily identified by its distinctive alternating light and dark bands, known as gneissic banding. Found worldwide in ancient shield areas and core mountain ranges.
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