metamorphic
Gneiss with Quartz Veining
Gneiss (High-grade Metamorphic Rock)
Hardness: 6-7 Mohs; Color: Dark grey to black matrix with reddish-tan quartz/feldspar banding; Luster: Dull to vitreous; Crystal Structure: Coarse-grained foliation; Specific Gravity: 2.6-2.9
- Hardness
- 6-7 Mohs
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black matrix with reddish-tan quartz/feldspar banding; Luster: Dull to vitreous; Crystal Structure: Coarse-grained foliation; Specific Gravity: 2.6-2.9
Formation & geological history
Formed through high-pressure, high-temperature regional metamorphism of igneous or sedimentary protoliths, often during mountain-building events. The specific banding suggests recrystallization and segregation of minerals.
Uses & applications
Used primarily as crushed stone for road construction, landscaping, and occasionally as architectural dimension stone (ornamental facing) if the patterns are striking.
Geological facts
Gneiss is one of the oldest rock types on Earth, with some specimens like the Acasta Gneiss dating back over 4 billion years. The banding is called 'gneissic banding'.
Field identification & locations
Identify by its distinct light and dark parallel banding (foliation). Commonly found in the crystalline cores of mountain ranges or in glacial tills. Collectors look for unique inclusions or sharp color contrasts.
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