metamorphic
Gneiss
Gneiss
Hardness: 6-7 on Mohs scale; Color: Banded gray, white, and brownish-tan; Luster: Dull to vitreous; Structure: Foliated with distinct bands (gneissic banding); Cleavage: Poor; Specific Gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Color
- Banded gray, white, and brownish-tan
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Banded gray, white, and brownish-tan; Luster: Dull to vitreous; Structure: Foliated with distinct bands (gneissic banding); Cleavage: Poor; Specific Gravity: 2.6-2.9.
Formation & geological history
Formed by high-grade regional metamorphism of pre-existing igneous or sedimentary rocks (like granite or shale) subjected to intense heat and pressure deep within the Earth's crust. It is often of Precambrian or Paleozoic age.
Uses & applications
Used as a crushed stone in road construction, as dimension stone for building facades, counter tops, and as decorative landscaping stone.
Geological facts
Gneiss is one of the oldest known rock types on Earth, with some specimens from the Acasta Gneiss in Canada dating back over 4 billion years.
Field identification & locations
Identified in the field by its distinct alternating layers of light and dark minerals. Commonly found in the cores of mountain ranges and eroded crystalline shields. Look for 'zebra-stripe' patterns.
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