metamorphic
Banded Gneiss with Quartz Vein
Foliated Metamorphic Rock (Gneiss)
Hardness: 6-7 (Mohs scale), Color: Dark grey, charcoal, and brown bands with a white quartz stripe, Luster: Dull/earthy for the matrix with a vitreous vein, Crystal Structure: Granular/crystalline, Cleavage: None (fractures irregularly)
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey, charcoal, and brown bands with a white quartz stripe, Luster: Dull/earthy for the matrix with a vitreous vein, Crystal Structure: Granular/crystalline, Cleavage: None (fractures irregularly)
Formation & geological history
Formed through high-pressure and high-temperature metamorphism of pre-existing igneous or sedimentary rocks. The white line is a hydrothermal quartz vein formed when silica-rich fluids filled a fracture during the cooling process.
Uses & applications
Primarily used in construction as crushed stone or landscaping gravel; larger polished pieces are used for architectural cladding or as decorative garden stones.
Geological facts
Gneiss is often among the oldest rocks found on Earth, with some specimens dating back over 4 billion years. The banding is caused by the segregation of minerals into layers under intense tectonic stress.
Field identification & locations
Identify by looking for distinct mineral banding and the presence of a hard, white crystalline vein that cannot be scratched by a steel nail. Commonly found in riverbeds and on beaches in glacially active regions.
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