metamorphic

Granite Gneiss

Felsic Gneiss (composed of Quartz, Feldspar, and Biotite)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale. Color: Pinkish-orange (orthoclase), grey (quartz), and black (biotite/hornblende). Luster: Dull to vitreous. Structure: Phaneritic with faint foliation or banding. Specific Gravity: 2.6-2.7.

Hardness: 6-7 on Mohs scale
Luster: Dull to vitreous

Identified June 20, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed through high-grade regional metamorphism of an igneous protolith (granite). Deep burial and high pressure/temperature cause the minerals to recrystallize and align into bands. Many specimens date to the Precambrian era.

Uses & applications

Used in heavy construction, as road aggregate, architectural stone, for monuments, and occasionally as landscaping stone.

Geological facts

Gneiss is one of the oldest known rock types on Earth; the Acasta Gneiss in Canada is approximately 4.03 billion years old. Because of its hardness, it is highly resistant to erosion.

Field identification & locations

Identify by its 'salt and pepper' or banded appearance and extreme hardness (cannot be scratched by a steel knife). Look for it in glaciated regions as 'glacial erratics' or in mountain belts like the Appalachians or Canadian Shield.