metamorphic
Gneiss
Foliated Metamorphic Rock
Hardness: 6-7 on Mohs scale; Color: Alternating light (quartz/feldspar) and dark (biotite/hornblende) bands, grey-white; Luster: Vitreous to dull; Texture: Medium to coarse-grained foliated texture.
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Alternating light (quartz/feldspar) and dark (biotite/hornblende) bands, grey-white; Luster: Vitreous to dull; Texture: Medium to coarse-grained foliated texture.
Formation & geological history
Formed by high-grade regional metamorphism of pre-existing sedimentary (shale/sandstone) or igneous (granite) rocks subjected to intense pressure and temperature deep within the Earth's crust.
Uses & applications
Used widely as crushed stone in construction, road aggregates, dimension stone for building facades, countertops, and landscaping.
Geological facts
The oldest known intact rocks on Earth, such as the Acasta Gneiss in Canada, are gneisses dated to approximately 4.03 billion years old.
Field identification & locations
Identified in the field by its distinctive 'gneissic banding'—alternating light and dark mineral layers. Common in mountainous regions and exposed Precambrian shield areas.
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