metamorphic
Gneiss (Banded Gneiss Cobble)
Gneiss
Hardness: 6-7 on Mohs scale. Color: Light grey to white matrix with contrasting dark grey to black mineral bands. Luster: Dull to earthy (weathered surface). Structure: Medium to coarse-grained metamorphic foliation with swirling or folded mineral segregation.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to earthy (weathered surface)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Light grey to white matrix with contrasting dark grey to black mineral bands. Luster: Dull to earthy (weathered surface). Structure: Medium to coarse-grained metamorphic foliation with swirling or folded mineral segregation.
Formation & geological history
Formed through high-grade regional metamorphism of igneous (granite) or sedimentary protoliths under extreme temperature and pressure. The characteristic swirling bands reflect intense ductile deformation during tectonic events.
Uses & applications
Used primarily as decorative garden stones, landscaping river rocks, crushed stone aggregate, and dimension stone.
Geological facts
The distinctive light and dark bands are called 'gneissic banding', resulting from the segregation of felsic (quartz, feldspar) and mafic (biotite, amphibole) minerals under extreme directional stress.
Field identification & locations
Identified field-wise by distinct alternating mineral bands and rounded cobble shape from water erosion. Commonly found in glaciated terrains, riverbeds, and mountainous regions with exposed Precambrian basement rock.
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