metamorphic
Gneiss
Gneiss (High-grade metamorphic rock)
Hardness: 6-7 on Mohs scale; Color: Gray, pink, or brownish with distinct light and dark banding; Luster: Variable (dull to vitreous); Crystal structure: Coarse-grained foliated; Cleavage: Poorly defined along bands
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, pink, or brownish with distinct light and dark banding
- Luster
- Variable (dull to vitreous)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray, pink, or brownish with distinct light and dark banding; Luster: Variable (dull to vitreous); Crystal structure: Coarse-grained foliated; Cleavage: Poorly defined along bands
Formation & geological history
Formed by high-pressure and high-temperature metamorphosis of igneous (granite) or sedimentary rocks. It often represents the highest grade of regional metamorphism.
Uses & applications
Used in construction as dimension stone for buildings, paving, and occasionally as decorative stone for countertops or landscaping.
Geological facts
Gneiss contains some of the oldest known rock on Earth, such as the Acasta Gneiss in Canada which is roughly 4.03 billion years old.
Field identification & locations
Identify in the field by looking for 'gneissose banding'—distinct parallel layers of different mineral colors. Commonly found in the cores of mountain ranges and ancient continental shields.
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