metamorphic
Banded Gneiss Pebble
Gneiss (Metamorphic Rock)
Hardness: 6-7 on Mohs scale; Color: Alternating dark (biotite/hornblende) and light (quartz/feldspar) bands with a quartz vein cross-cutting; Luster: Dull to vitreous; Texture: Medium to coarse-grained, foliated (gneissic banding).
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Alternating dark (biotite/hornblende) and light (quartz/feldspar) bands with a quartz vein cross-cutting; Luster: Dull to vitreous; Texture: Medium to coarse-grained, foliated (gneissic banding).
Formation & geological history
Formed by high-grade regional metamorphism of pre-existing sedimentary or igneous rocks subjected to extreme temperature and pressure deep within Earth's crust. Later eroded and rounded by stream or beach action into a pebble.
Uses & applications
Used as crushed stone in construction, decorative garden landscaping, and collected as beach/river pebbles.
Geological facts
The distinct banding (gneissic foliation) results from the segregation of dark mafic minerals and light felsic minerals under immense directional pressure.
Field identification & locations
Identified by distinct alternating light and dark mineral bands, often cross-cut by quartz or feldspar veins. Commonly found on riverbeds, glacial tills, and rocky beaches worldwide.
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