metamorphic
Gneiss
Gneiss
Hardness of 6-7 on the Mohs scale, characterized by distinctive alternating light and dark bands (gneissic banding), vitreous to dull luster, foliated crystal structure, specific gravity around 2.6-2.9.
Identified More metamorphic →
Explore Gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness of 6-7 on the Mohs scale, characterized by distinctive alternating light and dark bands (gneissic banding), vitreous to dull luster, foliated crystal structure, specific gravity around 2.6-2.9.
Formation & geological history
Formed by high-grade regional metamorphism, where pre-existing igneous or sedimentary rocks (such as granite or shale) are subjected to extreme heat and directed pressure deep within the Earth's crust.
Uses & applications
Commonly used as dimension stone in construction, facing stone for buildings, paving, and occasionally for landscaping and decorative gravel.
Geological facts
Gneiss includes some of the oldest rocks found on Earth, with certain formations dating back over 4 billion years, such as the Acasta Gneiss in Canada.
Field identification & locations
Easily identified in the field by its striking compositional banding (zebra-like stripes of light quartz/feldspar and dark biotite/amphibole). Found globally in ancient shield areas and core mountain ranges.
More like this
