metamorphic

Gneiss

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Pinkish-tan with dark grey/black bands; Luster: Dull to vitreous; Crystal Structure: Foliated with distinct banding (gneissic foliation); Cleavage: Poor; Specific Gravity: 2.6-2.9

Hardness: 6-7 on Mohs scale
Color: Pinkish-tan with dark grey/black bands
Luster: Dull to vitreous

Identified May 28, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under high temperature and pressure. Often Precambrian in age.

Uses & applications

Used as a crushed stone for road construction, as dimension stone for architectural facings and flooring, and as landscaping material.

Geological facts

Gneiss is one of the oldest rock types on Earth; the Acasta Gneiss in Canada is approximately 4 billion years old. The term comes from the Middle High German verb 'gneist' meaning 'to spark'.

Field identification & locations

Identified by alternating bands of light and dark minerals (foliation). Look for coarse grains and visible layering without easy split-ability like schist. Found globally in the cores of mountain ranges and ancient continental shields.