metamorphic
Banded Gneiss
Gneiss (High-grade regional metamorphic rock)
Hardness: 6.5-7 (Mohs); Color: Black and grey/white bands; Luster: Dull to vitreous; Crystal Structure: Coarse-grained foliated; Cleavage: Poor, but splits along bands; Specific Gravity: 2.6-2.9
- Hardness
- 6
- Color
- Black and grey/white bands
- Luster
- Dull to vitreous
Identified More metamorphic →
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Black and grey/white bands; Luster: Dull to vitreous; Crystal Structure: Coarse-grained foliated; Cleavage: Poor, but splits along bands; 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 distinct bands through recrystallization.
Uses & applications
Used primarily as decorative stone, crushed stone for road construction, building facades, and occasionally for high-end sculptures or countertops.
Geological facts
Gneiss contains some of the oldest rocks on Earth, such as the Acasta Gneiss in Canada which is nearly 4 billion years old. The term comes from the German word meaning 'sparkling' or 'to glow'.
Field identification & locations
Identified by its characteristic 'gneissic banding' where light and dark minerals are separated. Commonly found in the cores of mountain ranges and ancient continental shields. Look for alternating bands of quartz/feldspar and biotite/hornblende.
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