metamorphic

Banded gneiss (possibly migmatitic gneiss)

Quartz–feldspar–mica gneiss; composition commonly includes quartz, feldspar, biotite/hornblende, and accessory dark minerals

AI-generated identification · may be incorrect

Typically medium–coarse grained with strongly alternating light and dark mineral bands; vitreous quartz, feldspathic patches, and dark mica/amphibole. Hardness is about 6–7 Mohs, with weak-to-moderate foliation and irregular fracture; the specimen appears naturally weathered and iron-stained.

Identified August 18, 2026More metamorphic →

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At a glance

Common name: Banded gneiss (possibly migmatitic gneiss)
Scientific name: Quartz–feldspar–mica gneiss; composition commonly includes quartz, feldspar, biotite/hornblende, and accessory dark minerals
Category: metamorphic
Identified: August 18, 2026
Method: Standard

AI Estimated Value

About $2–$15 for a small common hand specimen; $20–$75 if unusually patterned, polished, or locality-documented.

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 preexisting igneous or sedimentary rocks underwent high-temperature, high-pressure metamorphism, causing minerals to recrystallize and segregate into bands. Such rocks commonly formed deep in Precambrian to Paleozoic continental crust, though exact age requires locality data.

Uses & applications

Used as crushed stone, aggregate, building stone, and decorative dimension stone; attractive polished pieces are collected but are generally not gemstone-grade.

Geological facts

The banding records metamorphic deformation and mineral segregation, often preserving multiple episodes of crustal heating and compression. Light layers are usually quartz/feldspar-rich, while dark layers contain mica or amphibole.

Field identification & locations

Identify it by persistent alternating light and dark bands, interlocking grains, and a hard, nonporous texture; distinguish it from striped sedimentary rock by its crystalline fabric and disrupted or folded banding. Common in ancient continental shields and regional metamorphic belts.