metamorphic
Foliated Metamorphic Rock (likely Gneiss or Schist)
Gneissic Metamorphic Rock
Mohs hardness: 6-7; Color: Orange, peach, and black banding; Luster: Dull to vitreous; Crystal structure: Primarily coarse grains in bands; Cleavage: Poor, but splits along foliation planes; Specific gravity: 2.6-2.9
- Hardness
- 6-7
- Color
- Orange, peach, and black banding
- Luster
- Dull to vitreous
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Physical properties
Mohs hardness: 6-7; Color: Orange, peach, and black banding; Luster: Dull to vitreous; Crystal structure: Primarily coarse grains in bands; Cleavage: Poor, but splits along foliation planes; Specific gravity: 2.6-2.9
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and pressure. Most are Proterozoic to Paleozoic in age.
Uses & applications
Used in construction as crushed stone, dimension stone for countertops and flooring, and sometimes as landscaping rock.
Geological facts
Gneiss can sometimes be older than the continents themselves; the Acasta Gneiss is one of the oldest known crustal rocks on Earth at roughly 4 billion years old.
Field identification & locations
Identify in the field by looking for distinct mineral banding (gneissic foliation) where light and dark minerals segregate into layers. Commonly found in the roots of mountain ranges and stable continental shields.
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