metamorphic
Banded Gneiss
Gneiss (High-grade Regional Metamorphic Rock)
Hardness: 6-7 on Mohs scale; Color: Contrasting light (white/gray/pink) and dark (black/brown) bands; Luster: Vitreous to dull; Crystal structure: Coarse-grained phaneritic; Cleavage: Poorly defined foliated planes; Specific gravity: 2.6-3.0.
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to dull
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: Contrasting light (white/gray/pink) and dark (black/brown) bands; Luster: Vitreous to dull; Crystal structure: Coarse-grained phaneritic; Cleavage: Poorly defined foliated planes; Specific gravity: 2.6-3.0.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous rocks (like granite) or sedimentary rocks (like shale) under intense heat (600-700°C) and pressure. This process causes mineral recrystallization and segregates minerals into distinct bands.
Uses & applications
Used primarily as crushed stone for road construction and concrete aggregate. High-quality specimens with attractive banding are used for architectural tiling, countertops, and ornamental landscaping stones.
Geological facts
Gneiss can contain some of the oldest rocks on Earth, such as the Acasta Gneiss in Canada which is roughly 4 billion years old. The term 'gneiss' originates from an Old High German word meaning 'sparkling' or 'to glisten.'
Field identification & locations
Identify in the field by looking for 'gneissic banding'—alternating layers of light silicate minerals (quartz/feldspar) and dark mafic minerals (biotite/amphibole). It differs from schist by having thicker layers and fewer mica flakes. Commonly found in the cores of mountain ranges and ancient continental shields.
More like this
