metamorphic
Banded Gneiss
Banded Orthogneiss or Paragneiss (Quartz-Feldspathic Gneiss)
Hardness: 6-7 (Mohs scale); Color: Variegated brown, tan, and white bands; Luster: Dull to sub-vitreous; Crystal structure: Coarse-grained foliated; Cleavage: Generally poor, breaks along foliations.
- Hardness
- 6-7 (Mohs scale)
- Color
- Variegated brown, tan, and white bands
- Luster
- Dull to sub-vitreous
Identified More metamorphic →
Explore Banded Gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs scale); Color: Variegated brown, tan, and white bands; Luster: Dull to sub-vitreous; Crystal structure: Coarse-grained foliated; Cleavage: Generally poor, breaks along foliations.
Formation & geological history
Formed under high-grade regional metamorphism where pre-existing rocks (igneous or sedimentary) were subjected to intense heat and pressure, causing minerals to segregate into distinct light and dark bands (gneissic banding).
Uses & applications
Used in construction as crushed stone, dimension stone for countertops and flooring, and occasionally as decorative landscaping rock or tumbled stones for collectors.
Geological facts
Gneiss is one of the oldest known rock types on Earth; the Acasta Gneiss in Canada is approximately 4 billion years old. The banding is a result of structural deformation rather than sedimentary layering.
Field identification & locations
Identified by prominent alternating bands of different mineral compositions. Found commonly in the roots of mountain ranges and ancient continental shields. Look for the 'salty and pepper' appearance of mica, quartz, and feldspar.
More like this
