metamorphic
Gneiss (Banded Gneiss)
Gneiss
Hardness: 6-7 (Mohs); Color: Alternating bands of grey, black, and white; Luster: Dull to vitreous; Structure: Foliated with distinct banding (gneissose banding); Cleavage: Poor; Specific Gravity: 2.6-2.9.
- Hardness
- 6-7 (Mohs)
- Color
- Alternating bands of grey, black, and white
- 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 (Mohs); Color: Alternating bands of grey, black, and white; Luster: Dull to vitreous; Structure: Foliated with distinct banding (gneissose banding); Cleavage: Poor; Specific Gravity: 2.6-2.9.
Formation & geological history
Formed by high-grade regional metamorphism of igneous (granite) or sedimentary (shale/sandstone) protoliths under intense heat and pressure. Often Precambrian and found in the crystalline basement of continental crust.
Uses & applications
Used in construction as crushed stone for road bases and concrete, as ornamental stone for countertops and flooring, and as landscaping material.
Geological facts
Gneiss is some of the oldest rock on Earth; the Acasta Gneiss in Canada is approximately 4 billion years old. The banding is caused by the segregation of light minerals (quartz/feldspar) and dark minerals (biotite/amphibole).
Field identification & locations
Identify by distinct 'zebra-stripe' layers. Unlike schist, it does not split easily along planes. Often found in mountainous regions or glacially deposited cobbles near rivers.
More like this
