metamorphic
Gneiss
Gneiss (High-grade metamorphic rock)
Hardness: 6-7 on Mohs scale; Color: Distinct light and dark bands (foliation); Luster: Dull to vitreous; Structure: Coarse-grained, crystalline with a foliated texture called 'gneissose banding'; Cleavage: Poorly defined.
- Hardness
- 6-7 on Mohs scale
- Color
- Distinct light and dark bands (foliation)
- Luster
- Dull to vitreous
Identified More metamorphic →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 on Mohs scale; Color: Distinct light and dark bands (foliation); Luster: Dull to vitreous; Structure: Coarse-grained, crystalline with a foliated texture called 'gneissose banding'; Cleavage: Poorly defined.
Formation & geological history
Formed under high-temperature and high-pressure conditions through the regional metamorphism of pre-existing igneous rocks (like granite) or sedimentary rocks. It represents one of the highest grades of metamorphism.
Uses & applications
Primary use is in construction as crushed stone for road bases and as dimension stone for architectural facades, countertops, and flooring.
Geological facts
Gneiss contains some of the oldest known rocks on Earth, such as the Acasta Gneiss in Canada, which is approximately 4.03 billion years old.
Field identification & locations
Identify by looking for 'salty and peppery' alternating bands of minerals like quartz/feldspar (light) and biotite/hornblende (dark). Common in mountainous regions and continental shields.
More like this
