metamorphic
Gneiss
Gneiss (Metamorphic Silicate)
AI-generated identification · may be incorrectHardness 6-7 on Mohs scale; distinctive alternating light and dark compositional banding (gneissic banding); vitreous luster; granular crystal structure with no distinct cleavage.
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Physical properties
Hardness 6-7 on Mohs scale; distinctive alternating light and dark compositional banding (gneissic banding); vitreous luster; granular crystal structure with no distinct cleavage.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under extreme heat and pressure, typically during continental collisions.
Uses & applications
Used primarily as crushed stone for construction, road aggregates, and occasionally as dimensional stone or building facades.
Geological facts
Gneiss contains some of the oldest known rocks on Earth, with certain formations dating back over 4 billion years.
Field identification & locations
Easily identified in the field by its striking zebra-like mineral bands; commonly found in ancient shield areas and deeply eroded mountain belts.
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