metamorphic
Gneiss with Quartz Veining
Gneiss (High-grade Metamorphic Rock)
Hardness: 6-7 on Mohs scale; Color: Gray, white, and tan with rusty iron staining; Luster: Dull to vitreous (on quartz parts); Structure: Foliated (banded or layered) with coarse grains; Cleavage: None, irregular fracture.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, white, and tan with rusty iron staining
- Luster
- Dull to vitreous (on quartz parts)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray, white, and tan with rusty iron staining; Luster: Dull to vitreous (on quartz parts); Structure: Foliated (banded or layered) with coarse grains; Cleavage: None, irregular fracture.
Formation & geological history
Formed through high-grade regional metamorphism of igneous or sedimentary protoliths under intense heat and pressure. The visible white veins are quartz that precipitated from hydrothermal fluids in fractures.
Uses & applications
Used primarily as crushed stone for road construction and as decorative garden boulders. High-quality slabs are used for countertops and building facades.
Geological facts
Gneiss is one of the oldest types of rock on Earth, with some specimens in Canada dated to over 4 billion years old. The distinct banding is called 'gneissose banding'.
Field identification & locations
Identify by looking for distinct layers (foliation) and coarse mineral grains. Common in mountainous regions and areas with ancient continental shields. Check for 'salty-and-pepper' mineral appearance.
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