metamorphic
Gneiss
Gneiss
Hardness: 6-7 on Mohs scale; Color: typically banded with dark and light layers (greenish-black and yellow-tan in this specimen); Luster: dull to vitreous; Crystal structure: crystalline but with a foliated, banded texture; Cleavage: poor; Specific gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Luster
- dull to vitreous
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: 6-7 on Mohs scale; Color: typically banded with dark and light layers (greenish-black and yellow-tan in this specimen); Luster: dull to vitreous; Crystal structure: crystalline but with a foliated, banded texture; Cleavage: poor; Specific gravity: 2.6-2.9.
Formation & geological history
Formed by high-grade regional metamorphism of pre-existing igneous or sedimentary rocks. The intense heat and pressure cause minerals to segregate into bands. These are often billions or hundreds of millions of years old.
Uses & applications
Commonly used as a decorative building stone, for flooring, gravestones, and as crushed stone or aggregate for road construction due to its durability.
Geological facts
Gneiss is some of the oldest rock on Earth, with the Acasta Gneiss in Canada being one of the oldest known crustal rocks at over 4 billion years old. The term comes from an Old High German word meaning 'sparkling' or 'to glitter'.
Field identification & locations
Identified by 'gneissose banding,' which are distinct bands of varying mineral composition. It can be found globally in the cores of mountain ranges and eroded crystalline shields. Look for the 'swirled' or striped layers when the rock is wet.
More like this
