metamorphic
Gneiss
Gneiss
Hardness: 6-7 on Mohs scale; Color: Grey and white banded; Luster: Variable, often dull with sparkling mineral grains; Structure: Foliated with distinct bands of minerals; Cleavage: None, breaks irregularly.
- Hardness
- 6-7 on Mohs scale
- Color
- Grey and white banded
- Luster
- Variable, often dull with sparkling mineral grains
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Grey and white banded; Luster: Variable, often dull with sparkling mineral grains; Structure: Foliated with distinct bands of minerals; Cleavage: None, breaks irregularly.
Formation & geological history
Formed through high-grade regional metamorphism of igneous or sedimentary rocks under intense heat and pressure, typically during mountain-building events.
Uses & applications
Used as building stone, decorative landscaping, and occasionally as crushed stone for aggregate in road construction.
Geological facts
The Gneissic banding is a result of mineral segregation where light and dark minerals separate into layers. The Acasta Gneiss in Canada is one of the oldest known rock units on Earth, at roughly 4 billion years old.
Field identification & locations
Identify by visible color-coordinated stripes (foliation) and lack of distinct cleavage. Often found in continental shields and core of mountain ranges. Collectors look for unique banding patterns.
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