metamorphic
Granitoid Gneiss with Feldspar Vein
Gneiss (High-grade Metamorphic Rock) with Potassium Feldspar (KAlSi3O8)
Hardness: 6-7 (Mohs), Color: Dark grey matrix with salmon-pink vein, Luster: Vitreous to dull, Crystal Structure: Foliated with crystalline bands, Cleavage: Two directions at 90 degrees in the feldspar grains, Specific Gravity: 2.6-2.9
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Physical properties
Hardness: 6-7 (Mohs), Color: Dark grey matrix with salmon-pink vein, Luster: Vitreous to dull, Crystal Structure: Foliated with crystalline bands, Cleavage: Two directions at 90 degrees in the feldspar grains, Specific Gravity: 2.6-2.9
Formation & geological history
Formed via high-pressure, high-temperature regional metamorphism of igneous or sedimentary protoliths, often during mountain-building events. The pink vein represents a late-stage hydrothermally deposited or pegmatitic intrusion of feldspar into a fracture.
Uses & applications
Metamorphic gneiss is commonly used in crushed stone for construction, as road base, and high-quality polished slabs are used for countertops and architectural cladding.
Geological facts
Gneiss makes up some of the oldest bedrock on Earth, including the Acasta Gneiss in Canada, which is approximately 4.03 billion years old. The 'pink' color in the vein is due to trace amounts of iron or structural defects within the Orthoclase lattice.
Field identification & locations
Identify in the field by looking for distinct banding (foliation) and the presence of hard, pink blocky crystals within dark host rock. Commonly found in Canadian Shield, Appalachians, and deeply eroded continental interiors.
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