metamorphic
Gneiss
Gneiss
Hardness: 6-7 on Mohs scale; Color: Banded gray, brown, and tan; Luster: Dull to vitreous; Structure: Foliated with alternating dark and light mineral bands; Cleavage: Poor; Specific gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Color
- Banded gray, brown, and tan
- 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: Banded gray, brown, and tan; Luster: Dull to vitreous; Structure: Foliated with alternating dark and light mineral bands; Cleavage: Poor; Specific gravity: 2.6-2.9.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing sedimentary or igneous rocks under intense heat and pressure, often within the roots of mountain ranges. Geological age varies greatly from Precambrian to Cenozoic.
Uses & applications
Used as a decorative stone in construction (flooring, facing, gravestones), as crushed stone for road bases, and occasionally as a landscape rock.
Geological facts
Gneiss is one of the oldest known rock types on Earth, with some specimens like the Acasta Gneiss dating back over 4 billion years. Its characteristic banding is called 'gneissic foliation'.
Field identification & locations
Identify in the field by its distinct color banding (segregation of minerals) and coarse grain size. It is common in the cores of mountain ranges and eroded shield areas like the Canadian Shield.
More like this
