Granite Gneiss

Physical Properties

Hardness: 6-7 on Mohs scale. Color: White, gray, and black. Luster: Dull to vitreous. Crystal structure: Medium to coarse-grained with foliation (banding). Cleavage: Poor. Specific gravity: 2.6-2.9.

Formation & Geological History

Formed through the high-grade regional metamorphism of igneous rocks like granite or sedimentary rocks like shale. The distinctive banding occurs under high heat and pressure, causing minerals to segregate into layers.

Uses & Applications

Used in construction as crushed stone, dimension stone for countertops and flooring, and occasionally as decorative landscaping pebbles or river rock.

Geological Facts

Gneiss is one of the oldest known rock types on Earth, with some specimens in Northern Canada dated to over 4 billion years old. It makes up a large portion of the Earth's lower continental crust.

Field Identification & Locations

Identify in the field by looking for 'gneissose banding,' which are alternating light (felsic) and dark (mafic) layers. It is ubiquitous in mountainous regions and shield areas globally.

Identified on: 4/15/2026

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