metamorphic
Gneiss
Metamorphic Gneiss (High-grade regional metamorphism)
Hardness: 6-7 Mohs; Color: Alternating bands/patches of grey, white, and black; Luster: Vitreous to dull; Crystal structure: Coarse-grained foliated texture; Specific Gravity: 2.6-2.9
- Hardness
- 6-7 Mohs
- Color
- Alternating bands/patches of grey, white, and black
- Luster
- Vitreous to dull
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/patches of grey, white, and black; Luster: Vitreous to dull; Crystal structure: Coarse-grained foliated texture; Specific Gravity: 2.6-2.9
Formation & geological history
Formed through high-grade regional metamorphism of igneous or sedimentary precursor rocks (protoliths) under intense heat and pressure, often at convergent plate boundaries. Most specimens are hundreds of millions to billions of years old.
Uses & applications
Used as a dimension stone for architectural facings, flooring, and curbing. Also crushed for use as road aggregate and in heavy construction projects.
Geological facts
Gneiss is one of the most common rocks in the Earth's crust. It often forms the 'basement' of continents and some of the oldest known rocks on Earth are Acasta Gneiss, dated to about 4 billion years.
Field identification & locations
Identified by 'gneissose banding' or distinct segregation of light and dark minerals. Common in mountain ranges and ancient shield areas. For collectors, look for well-defined mineral separation and large garnet or mica inclusions.
More like this
