metamorphic
Gneiss
Gneiss
Hardness: 6-7 on Mohs scale. Color: alternating light and dark bands (foliation). Luster: Dull to vitreous. Crystal structure: Coarse-grained, crystalline. Cleavage: Poor, but splits alongside bands. Specific gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Color
- alternating light and dark bands (foliation)
- Luster
- Dull to vitreous
Identified More metamorphic →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 on Mohs scale. Color: alternating light and dark bands (foliation). Luster: Dull to vitreous. Crystal structure: Coarse-grained, crystalline. Cleavage: Poor, but splits alongside bands. Specific gravity: 2.6-2.9.
Formation & geological history
Formed by high-grade regional metamorphism of pre-existing igneous or sedimentary rocks at high temperatures and pressures. Bands result from the segregation of minerals during recrystallization.
Uses & applications
Used as a crushed stone in construction for road bases and concrete; also used as a dimension stone for flooring, countertops, and gravestones.
Geological facts
Gneiss is one of the oldest known rock types on Earth, with some specimens from the Acasta Gneiss complex dated to over 4 billion years old.
Field identification & locations
Identify in the field by looking for 'gneissose banding' consisting of alternating layers of light minerals like quartz/feldspar and dark minerals like biotite/hornblende. Found globally in mountainous regions and continental shields.
More like this
