metamorphic

Banded Gneiss

Banded Gneiss (High-grade Metamorphic Rock)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Alternating light grey/white and dark grey/blue bands; Luster: Dull to slightly vitreous; Structure: Foliated (gneissic banding); Cleavage: Poor.

Hardness: 6-7 on Mohs scale
Color: Alternating light grey/white and dark grey/blue bands
Luster: Dull to slightly vitreous

Identified July 19, 2026More metamorphic →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Alternating light grey/white and dark grey/blue bands; Luster: Dull to slightly vitreous; Structure: Foliated (gneissic banding); Cleavage: Poor.

Formation & geological history

Formed from the high-grade regional metamorphism of pre-existing igneous or sedimentary rocks at extreme temperatures and pressures deep within the Earth's crust. Most specimens are Proterozoic or Archean in age.

Uses & applications

Commonly used as crushed stone in construction, road base, and occasionally as structural stone or decorative landscaping. High-quality slabs are sometimes used for countertops.

Geological facts

Gneiss represents one of the highest levels of metamorphism; its characteristic banding (gneissic foliation) occurs through a process called mineral segregation, where minerals separate into distinct layers.

Field identification & locations

Identified by 'ribbon-like' layering of alternating colors within a hard, crystalline matrix. Found in the cores of mountain ranges and ancient continental shields. Smooth, water-worn pebbles like this are common in riverbeds and glacial deposits.