metamorphic
Gneiss
Gneiss (High-grade Regional Metamorphic Rock)
Hardness: 6-7 (Mohs scale); Color: Typically alternating dark (mafic) and light (felsic) bands of gray, white, pink, and black; Luster: Dull to vitreous; Structure: Foliated with distinct gneissic banding; Specific Gravity: 2.6-2.9
- Hardness
- 6-7 (Mohs scale)
- 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 (Mohs scale); Color: Typically alternating dark (mafic) and light (felsic) bands of gray, white, pink, and black; Luster: Dull to vitreous; Structure: Foliated with distinct gneissic banding; Specific Gravity: 2.6-2.9
Formation & geological history
Formed through high-pressure, high-temperature regional metamorphism of igneous or sedimentary protoliths; typically found in the core of mountain ranges and ancient crystalline shields ranging from Proterozoic to Archean ages
Uses & applications
Used primarily as dimension stone in construction (crushed stone, flooring, gravestones, and countertops) due to its durability and aesthetic banding; also used as landscaping decorative rock
Geological facts
The Acasta Gneiss in the Canadian Northwest Territories is one of the oldest known crustal rocks on Earth, dated to approximately 4.03 billion years old
Field identification & locations
Identify in the field by looking for distinct mineral segregation into layers (foliation) where bands are relatively thick; commonly found in the Appalachian Mountains, Scandinavian Mountains, and the Canadian Shield
More like this
