metamorphic
Gneiss
Gneiss (High-grade metamorphic rock)
Hardness: 6-7 (Mohs scale), Color: Dark grey to black with white or cream-colored mineral bands, Luster: Dull to pearly, Crystal structure: Coarse-grained foliated, Cleavage: Poor, Specific gravity: 2.6-2.9
Identified More metamorphic →
Explore Gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey to black with white or cream-colored mineral bands, Luster: Dull to pearly, Crystal structure: Coarse-grained foliated, Cleavage: Poor, Specific gravity: 2.6-2.9
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and pressure. It often dates back to the Precambrian era depending on the locality.
Uses & applications
Used in construction for road aggregate, building stone, and decorative landscaping. High-quality specimens are sometimes used for countertops or ornamental carvings.
Geological facts
Gneiss is one of the oldest rock types found on Earth. The name comes from a German word meaning 'to spark' or 'glitter' due to its mineral content. The distinct layering seen is called 'gneissic banding'.
Field identification & locations
Identifiable by its distinct alternating layers of dark (biotite/amphibole) and light (quartz/feldspar) minerals. Found in mountainous regions or beach deposits as water-worn cobbles. Look for the 'zebra-stripe' appearance.
More like this
