metamorphic
Gneiss
High-grade metamorphic rock (Gneiss)
Hardness: 6-7 (Mohs scale); Color: alternating light (quartz/feldspar) and dark (biotite/amphibole) bands; Luster: dull to vitreous; Structure: foliated with coarse grain texture; Specific gravity: approx 2.6-2.9.
- Hardness
- 6-7 (Mohs scale)
- Luster
- dull to vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: alternating light (quartz/feldspar) and dark (biotite/amphibole) bands; Luster: dull to vitreous; Structure: foliated with coarse grain texture; Specific gravity: approx 2.6-2.9.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under extreme heat and pressure. This specimen displays river-tumbled rounding, indicating it was smoothed by water erosion.
Uses & applications
Used in construction as crushed stone for road bases, as dimension stone for architectural facades, countertops, and decorative landscaping.
Geological facts
Gneiss is among the oldest known rocks on Earth, with some specimens like the Acasta Gneiss dating back over 4 billion years. The specific wavy pattern seen here is a result of plastic deformation during metamorphism.
Field identification & locations
Identified by its distinctive 'gneissose banding' where minerals are segregated into dark and light layers. Commonly found in the crystalline cores of mountain ranges and stable continental shields.
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