metamorphic
Quartz Vein in Amphibolite / Gneiss
Quartz (SiO2) in Mafic Metamorphic Host Rock
Hardness: Quartz ~7, Host rock ~5-6 on Mohs scale. Luster: Vitreous to greasy (quartz), dull to glistening (host rock). Color: White/translucent quartz band contrasting with dark black/grey amphibole and biotite matrix. Structure: Crystalline quartz filling a fractures in coarse-grained foliated metamorphic rock.
- Hardness
- Quartz ~7, Host rock ~5-6 on Mohs scale
- Luster
- Vitreous to greasy (quartz), dull to glistening (host rock)
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Physical properties
Hardness: Quartz ~7, Host rock ~5-6 on Mohs scale. Luster: Vitreous to greasy (quartz), dull to glistening (host rock). Color: White/translucent quartz band contrasting with dark black/grey amphibole and biotite matrix. Structure: Crystalline quartz filling a fractures in coarse-grained foliated metamorphic rock.
Formation & geological history
Formed when silica-rich hydrothermal fluids circulated through fractures in dark mafic metamorphic rocks like amphibolite, basalt, or schist during high-pressure and high-temperature regional metamorphism. As the fluids cooled, quartz mineral crystals precipitated and filled the crack.
Uses & applications
Used primarily for educational rock specimens, geological mapping indicator, and local decorative stone. Quartz veins are also key exploration targets for precious metals like gold.
Geological facts
Quartz veins often crosscut older host rock formations, providing geologists with vital cross-cutting relationship evidence to determine relative geological age and deformation history.
Field identification & locations
Identified by the distinct sharp contact between milky or crystalline quartz and the surrounding dark mafic country rock. Found worldwide in metamorphic terranes such as the Appalachian or Alpine mountain belts. Value: $5-$25 for small hand specimens.
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