metamorphic
Gneiss
Metamorphic Gneiss (High-grade regional metamorphism)
Hardness: 6-7 Mohs; Color: Gray, pinkish-tan, and dark mica bands; Luster: Dull to vitreous; Structure: Foliated (gneissose banding); Gravity: 2.6-2.9
- Hardness
- 6-7 Mohs
- Color
- Gray, pinkish-tan, and dark mica bands
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Gray, pinkish-tan, and dark mica bands; Luster: Dull to vitreous; Structure: Foliated (gneissose banding); Gravity: 2.6-2.9
Formation & geological history
Formed from the high-grade regional metamorphism of pre-existing sedimentary or igneous rocks (like granite or shale) under intense heat and pressure, typically during mountain-building events.
Uses & applications
Used as a dimension stone for flooring, countertops, and grave markers; also crushed for road construction, landscaping, and aggregate.
Geological facts
Gneiss is one of the oldest rock types on Earth, with the Acasta Gneiss in Canada being estimated at approximately 4.03 billion years old.
Field identification & locations
Identify by looking for distinct alternating bands of light-colored (quartz/feldspar) and dark-colored (biotite/amphibole) minerals. Found in continental shields and mountain interiors.
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