metamorphic
Gneiss
Foliated Metamorphic Rock
Hardness: 6-7 on Mohs scale; Color: Gray, white, and brownish due to iron oxidation; Luster: Dull to vitreous; Crystal Structure: Coarse-grained with distinct mineral banding (foliation); Cleavage: Poorly defined along bands; Specific Gravity: 2.6-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, white, and brownish due to iron oxidation
- 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: Gray, white, and brownish due to iron oxidation; Luster: Dull to vitreous; Crystal Structure: Coarse-grained with distinct mineral banding (foliation); Cleavage: Poorly defined along bands; Specific Gravity: 2.6-3.0.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks at extreme temperatures and pressures. These are often found in the roots of mountain ranges and can date back to the Precambrian era.
Uses & applications
Commonly used as a decorative stone in architecture, as crushed stone for road construction, and for landscaping or gravestones due to its durability and aesthetic banding.
Geological facts
The Acasta Gneiss in Northwest Territories, Canada, is one of the oldest known intact crustal rock fragments on Earth, dated to approximately 4 billion years ago.
Field identification & locations
Identify in the field by looking for 'gneissose banding'—alternating light and dark layers of minerals like quartz, feldspar, and mica. It is found globally in continental shields and mountain belts.
More like this
