metamorphic

Gneiss (possibly migmatitic or strongly folded banded gneiss)

Banded quartz–feldspar–mica gneiss; variable composition, commonly quartz + plagioclase/alkali feldspar + biotite/muscovite ± amphibole

AI-generated identification · may be incorrect

Typically coarse-grained, gray to dark gray, with pronounced compositional banding and intensely folded foliation; vitreous quartz and pearly mica may be visible. Hardness is about 6–7 Mohs, with no consistent cleavage as a rock and specific gravity around 2.6–2.8.

Identified September 5, 2026More metamorphic →

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At a glance

Common name: Gneiss (possibly migmatitic or strongly folded banded gneiss)
Scientific name: Banded quartz–feldspar–mica gneiss; variable composition, commonly quartz + plagioclase/alkali feldspar + biotite/muscovite ± amphibole
Category: metamorphic
Identified: September 5, 2026
Method: Standard

AI Estimated Value

Common rough field specimens: $5–$30; attractive large, polished, or unusually folded specimens: approximately $50–$300.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Formed when granite, sedimentary rocks, or volcanic protoliths underwent high-grade metamorphism, commonly at amphibolite- to granulite-facies conditions during continental collision. Individual specimens may be Precambrian or younger, depending on locality.

Uses & applications

Used as dimension stone, paving, wall stone, aggregate, and decorative landscaping rock; attractive polished pieces are collected but are generally less valuable than gemstone material.

Geological facts

The image shows strong ductile deformation, producing contorted light and dark mineral bands. Gneiss differs from schist by its more compositional banding and generally coarser, less uniformly micaceous texture.

Field identification & locations

Identify it by alternating quartz–feldspar-rich and mica/amphibole-rich bands, strong foliation, and a granular crystalline texture; common in ancient continental shields and mountain belts worldwide. A firm identification may require a fresh surface or thin section.