Banded Gneiss

Physical Properties

Hardness: 6-7 (Mohs scale); Color: Banded layers of yellow-tan, dark grey, and green; Luster: Dull to sub-vitreous; Crystal structure: Coarse-grained phaneritic; Cleavage: Poor, usually breaks along foliation; Specific gravity: 2.6-2.9

Formation & Geological History

Formed through the high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and pressure deep within the Earth's crust, leading to the segregation of minerals into bands (foliation).

Uses & Applications

Used primarily as crushed stone for road construction, as ornamental stone in landscaping, or as building material for flooring, gravestones, and countertops.

Geological Facts

Gneiss is some of the oldest rock on Earth, with the Acasta Gneiss in Canada being dated to approximately 4 billion years old. The term comes from the German word 'Gneis', meaning spark.

Field Identification & Locations

Identify in the field by looking for 'gneissose banding' consisting of alternating light and dark mineral layers. Commonly found in the cores of mountain ranges and ancient continental shields. Collectors look for sharp contrast in bands.

Identified on: 5/2/2026

Mode: Standard