metamorphic
Banded Gneiss
Gneiss
Hardness: 6-7 on Mohs scale; Color: Gray with alternating dark and light bands; Luster: Dull to sub-vitreous; Structure: Foliated with distinct banding (gneissose), medium to coarse-grained; Specific Gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray with alternating dark and light bands
- Luster
- Dull to sub-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 with alternating dark and light bands; Luster: Dull to sub-vitreous; Structure: Foliated with distinct banding (gneissose), medium to coarse-grained; Specific Gravity: 2.6-2.9.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under extreme heat and pressure, causing minerals to segregate into bands. Often Precambrian in age.
Uses & applications
Used as crushed stone for road construction and railroad ballast; occasionally used for dimension stone, countertops, and decorative landscaping.
Geological facts
Gneiss contains some of the oldest known rock on Earth, such as the Acasta Gneiss in Canada which is roughly 4 billion years old. The term 'gneiss' comes from an Old German word meaning 'to spark' or 'bright'.
Field identification & locations
Identified by its distinctive light and dark color bands and lack of distinct cleavage. Common in the cores of mountain ranges and ancient continental shields. Look for 'stripes' that wrap around the rock.
More like this
