metamorphic
Gneiss with Quartz/Feldspar Vein
Quartz-Feldspathic Gneiss
Hardness: 6-7 on Mohs scale; Color: Dark grey/salt-and-pepper matrix with a pinkish-tan band; Luster: Dull to vitreous; Structure: Foliated with distinct mineral banding; Cleavage: None (fractures irregularly)
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey/salt-and-pepper matrix with a pinkish-tan band
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey/salt-and-pepper matrix with a pinkish-tan band; Luster: Dull to vitreous; Structure: Foliated with distinct mineral banding; Cleavage: None (fractures irregularly)
Formation & geological history
Formed by high-grade regional metamorphism of igneous or sedimentary protoliths under extreme pressure and temperature. The pink band represents a pegmatitic vein of quartz and orthoclase feldspar that intruded or segregated during the metamorphic process.
Uses & applications
Used in construction as crushed stone, dimension stone for countertops and flooring, and as landscaping decorative rocks.
Geological facts
Gneiss is one of the oldest rock types on Earth, with some specimens from the Acasta Gneiss complex dating back over 4 billion years. The banding is caused by the separation of light and dark minerals during intense pressure.
Field identification & locations
Identify by looking for distinct layers (foliation) and large mineral grains. Commonly found in the roots of mountain ranges or glacial till. The rounded shape indicates transport by water or ice.
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