Banded Gneiss

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Alternating light (feldspar/quartz) and dark (biotite/hornblende) bands; Luster: Dull to vitreous; Crystal structure: Foliated (gneissose banding); Specific gravity: 2.6-2.9.

Formation & Geological History

Formed through high-grade regional metamorphism of igneous or sedimentary rocks under intense heat and pressure. This process causes minerals to segregate into distinct layers or bands.

Uses & Applications

Used in construction as crushed stone or dimension stone (countertops, flooring), and occasionally as decorative landscaping stone.

Geological Facts

Gneiss is one of the oldest known rock types on Earth, with the Acasta Gneiss in Canada dating back approximately 4 billion years.

Field Identification & Locations

Identify in the field by its characteristic 'gneissose banding'—distinct parallel layers of different minerals. It is common in mountainous regions and continental shields like the Canadian Shield or the Appalachians.

Identified on: 4/28/2026

Mode: Standard