metamorphic
Granitic Gneiss
Gneiss (containing Potassium Feldspar and Quartz)
Hardness: 6-7 on Mohs scale; Color: Gray matrix with pink/salmon inclusions; Luster: Dull to vitreous; Structure: Foliated or crystalline; Cleavage: Poor; Specific Gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray matrix with pink/salmon inclusions
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray matrix with pink/salmon inclusions; Luster: Dull to vitreous; Structure: Foliated or crystalline; Cleavage: Poor; Specific Gravity: 2.6-2.9.
Formation & geological history
Formed through high-grade regional metamorphism of igneous granite or sedimentary protoliths under intense heat and pressure. The pink zones are likely Orthoclase (K-feldspar).
Uses & applications
Used primarily as crushed stone for road construction, concrete aggregate, and occasionally as dimension stone for countertops or monuments if the banding is aesthetic.
Geological facts
Gneiss is some of the oldest rock on Earth, with the Acasta Gneiss in Canada dating back over 4 billion years. It is characterized by 'gneissic banding', though in small fragments like this, it may appear as simple mineral segregation.
Field identification & locations
Identify by looking for distinct mineral layers or large crystals of feldspar embedded in a darker, finer-grained matrix. Commonly found in the roots of mountain ranges and Precambrian shield areas.
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