metamorphic
Pink Gneiss / Pink Granite Gneiss
Felsic Gneiss (dominated by Orthoclase Feldspar and Quartz)
Hardness: 6-7 on Mohs scale; Color: Pink, salmon, or peach with black streaks; Luster: Vitreous to dull; Crystal structure: Coarse-grained with distinct mineral banding (foliation); Cleavage: Perfect on feldspar grains; Specific gravity: 2.6-2.7
- Hardness
- 6-7 on Mohs scale
- Color
- Pink, salmon, or peach with black streaks
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Pink, salmon, or peach with black streaks; Luster: Vitreous to dull; Crystal structure: Coarse-grained with distinct mineral banding (foliation); Cleavage: Perfect on feldspar grains; Specific gravity: 2.6-2.7
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing granitic igneous rocks or sedimentary rocks at extreme pressure and temperature. The pink color comes from potassium-rich orthoclase feldspar, and the black bands are likely biotite mica or hornblende.
Uses & applications
Used as dimension stone for countertops, flooring, and decorative building facades. Smaller specimens are often tumbled for use in landscaping or collection.
Geological facts
Gneiss is one of the oldest known rock types on Earth, with some specimens in the Acasta Gneiss complex dating back over 4 billion years. The banding is caused by mineral segregation during intense metamorphic pressure.
Field identification & locations
Identified by 'gneissic banding' where dark and light minerals separate into layers. Look for the pink feldspar blocks coupled with black wavy lines. Found globally in ancient tectonic shield areas like the Canadian Shield or the Appalachian Mountains.
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