metamorphic
Gneiss (Metamorphic Rock)
Gneiss
Hardness: 6-7 on Mohs scale. Color: Gray, pink, or brownish with dark streaks. Luster: Dull to pearly. Crystal structure: Medium to coarse-grained. Cleavage: Poor, but exhibits distinct bands (foliation).
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, pink, or brownish with dark streaks
- Luster
- Dull to pearly
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, pink, or brownish with dark streaks. Luster: Dull to pearly. Crystal structure: Medium to coarse-grained. Cleavage: Poor, but exhibits distinct bands (foliation).
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks. Usually formed deep within the crust under extreme temperature and pressure conditions, often during mountain-building events.
Uses & applications
Used primarily in construction for crushed stone, road building, landscaping, and occasionally as dimension stone for countertops or gravestones due to its durability.
Geological facts
Gneiss is one of the oldest rocks on Earth; the Acasta Gneiss in Canada is approximately 4.03 billion years old. The term 'gneiss' comes from an Old High German verb meaning 'to spark' because the rock can glint in the light.
Field identification & locations
Identify in the field by looking for 'gneissose banding'—distinct layers of light and dark minerals. Common in the roots of mountain ranges and glacial deposits. Collectors value specimens with high-contrast banding.
More like this
