metamorphic
Gneiss
Metamorphic Gneiss
Hardness of 6-7 on the Mohs scale, characterized by distinctive alternating light and dark mineral bands (gneissic banding), vitreous to dull luster, granular crystal structure, specific gravity of 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 mineral bands (gneissic banding), vitreous to dull luster, granular crystal structure, specific gravity of 2.6-2.9.
Formation & geological history
Formed by high-temperature and high-pressure metamorphic processes acting on pre-existing igneous or sedimentary rocks (such as granite or shale) deep within the Earth's crust, often during continental collisions.
Uses & applications
Commonly used in the construction industry as crushed stone for road bases, building facades, and dimension stone for landscaping and flooring.
Geological facts
Some gneiss formations contain some of the oldest rocks found on Earth, dating back over 4 billion years, such as the Acasta Gneiss in Canada.
Field identification & locations
Easily identified in the field by its distinct compositional banding (light quartz/feldspar bands alternating with dark biotite/hornblende bands); commonly found in deeply eroded mountain belts and cratons.
More like this
