metamorphic
Quartz-veined Gneiss
Gneiss with Quartz (SiO2) intrusions
Hardness: 6-7 (Mohs scale), Color: Banded gray, black, and white/cream, Luster: Vitreous to dull, Crystal Structure: Foliated with crystalline veins, Cleavage: Poor, Specific Gravity: 2.6-2.9
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Banded gray, black, and white/cream, Luster: Vitreous to dull, Crystal Structure: Foliated with crystalline veins, Cleavage: Poor, Specific Gravity: 2.6-2.9
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks. The white bands represent quartz veins that intruded into fractures in the host rock during tectonic activity.
Uses & applications
Used primarily as crushed stone for construction, road base, and decorative landscaping. High-quality specimens are used in architectural stone and countertops.
Geological facts
The banding in gneiss is called gneissic foliation and is often the result of segregation of different minerals under extreme pressure and heat deep within the Earth's crust.
Field identification & locations
Identify in the field by looking for distinct layers (bands) of light and dark minerals. Quartz veins will be harder than a steel knife and will not react with acid. Commonly found in ancient mountain belts and glacial till.
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