metamorphic
Pink Granite Gneiss
Granitic Gneiss
Hardness: 6-7 (Mohs scale); Color: Pink, light gray, and black speckles; Luster: Dull to pearly; Crystal structure: Foliated, coarse-grained bands; Specific gravity: 2.6 - 2.9.
- Hardness
- 6-7 (Mohs scale)
- Color
- Pink, light gray, and black speckles
- Luster
- Dull to pearly
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Pink, light gray, and black speckles; Luster: Dull to pearly; Crystal structure: Foliated, coarse-grained bands; Specific gravity: 2.6 - 2.9.
Formation & geological history
Formed by high-grade regional metamorphism of igneous granite or sedimentary protoliths. It usually forms deep within the crust during mountain-building events (orogenies) at high temperature and pressure.
Uses & applications
Used in construction for road ballast, floor tiles, countertops, and decorative landscaping. High durability makes it ideal for architectural facing.
Geological facts
Gneiss is one of the oldest rock types on Earth, with some specimens in the Acasta Gneiss complex dated to over 4 billion years old. The distinctive banding is called 'gneissic banding'.
Field identification & locations
Identified by light and dark colored parallel bands and a coarse grain size. Commonly found in Scandinavian countries, Canada (Canadian Shield), and the Appalachian Mountains. Look for alternating layers of pink potassium feldspar and dark minerals.
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