metamorphic
Banded Gneiss / Metamorphic River Pebble
Gneiss (Foliated Metamorphic Rock)
Hardness: 6-7 on Mohs scale; Color: Grey with lighter quartz/feldspar and darker biotite/amphibole bands; Luster: Dull to silky; Texture: Fine-grained, stream-rounded with distinct compositional banding (gneissic foliation); Specific Gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to silky
Identified More metamorphic →
Explore Banded Gneiss / Metamorphic River Pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 on Mohs scale; Color: Grey with lighter quartz/feldspar and darker biotite/amphibole bands; Luster: Dull to silky; Texture: Fine-grained, stream-rounded with distinct compositional banding (gneissic foliation); Specific Gravity: 2.6-2.9.
Formation & geological history
Formed under high-grade regional metamorphism subjecting pre-existing sedimentary or igneous rocks to intense heat and pressure, causing mineral segregation into distinct light and dark bands. Subsequently weathered and rounded by river or ocean erosion.
Uses & applications
Commonly used in crushed stone aggregate, landscaping, road construction, and decorative river rocks.
Geological facts
Gneiss is among the oldest known rocks on Earth, with some specimens like the Acasta Gneiss in Canada dating back over 4 billion years.
Field identification & locations
Identified by alternating light (feldspar/quartz) and dark (biotite/amphibole) mineral bands paired with a water-worn, smooth pebble shape. Extremely common along riverbeds, glacial tills, and coastlines worldwide.
More like this
