Gneiss

Physical Properties

Hardness: 6-7 (Mohs scale), Color: Alternating light and dark bands (foliation), Luster: Dull to pearly, Crystal structure: Coarse-grained, non-distinct crystals, Cleavage: Poor, Specific gravity: 2.6-2.9

Formation & Geological History

Forms from the high-temperature and high-pressure metamorphism of granite or sedimentary rocks like shale; typically Precambrian or Paleozoic in age

Uses & Applications

Used as building stone, decorative landscaping, flooring, and crushed stone for road construction

Geological Facts

The Gneiss in the Acasta Gneiss complex in Canada is among the oldest known intact crustal rocks on Earth, dated to approximately 4.03 billion years

Field Identification & Locations

Identify by 'gneissose banding' or segregated layers of dark (biotite/hornblende) and light (quartz/feldspar) minerals. Found in mountainous regions and continental shields

Identified on: 5/11/2026

Mode: Standard