metamorphic
Gneiss
Metamorphic Gneiss
Hardness: 6-7 on the Mohs scale; Color: Gray, tan, white, and brownish tones with distinct compositional banding; Luster: Dull to vitreous; Structure: Foliated, medium to coarse-grained texture; Cleavage: Poor, fractures irregularly along mineral alignment.
- Hardness
- 6-7 on the 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 the Mohs scale; Color: Gray, tan, white, and brownish tones with distinct compositional banding; Luster: Dull to vitreous; Structure: Foliated, medium to coarse-grained texture; Cleavage: Poor, fractures irregularly along mineral alignment.
Formation & geological history
Formed under high-temperature and high-pressure regional metamorphism of pre-existing igneous rocks (like granite) or sedimentary rocks. Common in ancient crystalline shield areas and mountain cores worldwide.
Uses & applications
Used extensively as crushed stone for road base, aggregate in concrete, dimension stone for building facades, landscaping boulders, and decorative garden features.
Geological facts
Gneiss often features distinct alternating dark and light mineral bands known as 'gneissic banding.' The term comes from an old German mining word meaning 'sparkling' or 'bright.'
Field identification & locations
Identified in the field by visible parallel banding or stripes of quartz/feldspar (light) and biotite/amphibole (dark) without splitting easily like schist. Common along riverbeds, glacial deposits, and mountain ranges.
More like this
