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, granular texture.
- 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, granular texture.
Formation & geological history
Formed by high-temperature and high-pressure metamorphic processes acting on pre-existing igneous or sedimentary rocks (such as granite or shale), typically during regional mountain-building events.
Uses & applications
Commonly used as crushed stone for construction, building facades, landscaping, and decorative tiles.
Geological facts
Gneiss contains some of the oldest rocks found on Earth, dating back over 4 billion years in certain regions like the Acasta Gneiss in Canada.
Field identification & locations
Easily identified in the field by its distinct alternating dark and light compositional banding, known as gneissic banding.
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