metamorphic
Gneiss (Granitic Gneiss)
Gneiss
Hardness: 6-7 on Mohs scale. Color: Banded pink, white, gray, and black. Luster: Dull to vitreous. Crystal structure: Coarse-grained with distinct foliation (layering). Specific gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Color
- Banded pink, white, gray, and black
- 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: Banded pink, white, gray, and black. Luster: Dull to vitreous. Crystal structure: Coarse-grained with distinct foliation (layering). Specific gravity: 2.6-2.9.
Formation & geological history
Formed through high-grade regional metamorphism of granite or sedimentary rocks. Subjected to intense heat and pressure deep within the Earth's crust, leading to the segregation of minerals into bands.
Uses & applications
Used primarily as a building stone, for crushed stone in road construction, and for decorative landscape architecture and countertops (often sold as 'granite').
Geological facts
Gneiss is among the oldest known rocks on Earth; the Acasta Gneiss in Canada is approximately 4.03 billion years old. The name comes from the Middle High German verb 'gneist' (to spark).
Field identification & locations
Identify by 'gneissose banding'—distinct light and dark layers. Commonly found in the crystalline cores of mountain ranges and ancient continental shields (like the Canadian Shield or Appalachians).
More like this
