metamorphic
Banded Gneiss (with Quartz Vein)
Gneiss (Metamorphic rock of varying mineralogy)
Hardness: 6-7 on Mohs scale; Color: Black, dark grey, and white; Luster: Vitreous to dull; Crystal structure: Coarse-grained foliated texture with distinct bands; Specific Gravity: 2.6 - 3.0
- Hardness
- 6-7 on Mohs scale
- Color
- Black, dark grey, and white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Black, dark grey, and white; Luster: Vitreous to dull; Crystal structure: Coarse-grained foliated texture with distinct bands; Specific Gravity: 2.6 - 3.0
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks. The heat and pressure align minerals into 'gneissose banding.' The white bands are often quartz or feldspar segregations.
Uses & applications
Used in construction as crushed stone, dimension stone for countertops and flooring, and occasionally as decorative landscaping stones.
Geological facts
Gneiss is among the oldest known rocks on Earth, some dating back over 4 billion years (Acasta Gneiss). The characteristic banding is often more resistant to weathering than surrounding material.
Field identification & locations
Identify in the field by looking for 'layer cake' banding and visible minerals like quartz, mica, and feldspar. It is common in mountainous regions and riverbeds near ancient continental shields.
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