metamorphic
Gneiss
Gneiss
Hardness: 6-7 on Mohs scale; Color: typically banded gray, white, and pink; Luster: variable (dull to vitreous); Structure: foliated with coarse mineral grains and distinct banded layers (gneissose banding); Cleavage: poor.
- Hardness
- 6-7 on Mohs scale
- Color
- typically banded gray, white, and pink
- Luster
- variable (dull to vitreous)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: typically banded gray, white, and pink; Luster: variable (dull to vitreous); Structure: foliated with coarse mineral grains and distinct banded layers (gneissose banding); Cleavage: poor.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous rocks (like granite) or sedimentary rocks (like shale) at high temperatures and pressures deep within the Earth's crust.
Uses & applications
Used primarily in building construction as dimension stone for facades, flooring, and curbing, as well as crushed stone for road bases and landscaping.
Geological facts
Gneiss contains some of the oldest known rock on Earth, including the Acasta Gneiss in Canada, which is roughly 4.03 billion years old.
Field identification & locations
Identified in the field by its characteristic alternating bands of light-colored (felsic) and dark-colored (mafic) minerals. Found in the roots of mountain ranges and stable continental interiors (shields).
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