metamorphic
Banded Gneiss
Metamorphic Gneiss
Hardness: 6-7 (Mohs scale), Color: light grey with dark blue/black bands, Luster: dull to pearly, Structure: foliated with distinct banding (gneissic fabric), Specific Gravity: 2.6-2.9
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Physical properties
Hardness: 6-7 (Mohs scale), Color: light grey with dark blue/black bands, Luster: dull to pearly, Structure: foliated with distinct banding (gneissic fabric), Specific Gravity: 2.6-2.9
Formation & geological history
Formed by high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and pressure, typically in deep crustal environments during mountain-building events.
Uses & applications
Used primarily in heavy construction, road base, as decorative garden stone, and occasionally for countertops and floor tiles when high-quality slabs are found.
Geological facts
Gneiss contains some of the oldest known rock materials on Earth, such as the Acasta Gneiss in Canada, which is over 4 billion years old.
Field identification & locations
Identified by alternating light and dark mineral layers. Commonly found in the cores of mountain ranges and eroded crystalline shields. Collectors look for sharp, high-contrast banding.
