metamorphic

Dark gneiss or migmatitic amphibolite

Band ed gneiss; composition likely quartz–feldspar–biotite/amphibole, possibly migmatite

AI-generated identification · may be incorrect

Coarse-grained, dark gray to black rock with irregular pale quartz-feldspar bands or veins; minerals have vitreous to subvitreous luster. Hardness is approximately 6–7 Mohs, with strong foliation but no obvious cleavage at specimen scale; exact identification requires thin-section or mineral testing.

Identified September 22, 2026More metamorphic →

Explore Dark gneiss or migmatitic amphibolite in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

At a glance

Common name: Dark gneiss or migmatitic amphibolite
Scientific name: Band ed gneiss; composition likely quartz–feldspar–biotite/amphibole, possibly migmatite
Category: metamorphic
Identified: September 22, 2026
Method: Standard

AI Estimated Value

Approximately $5–$30 as a common hand specimen; $30–$100 or more if unusually attractive, locality-documented, or polished.

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 pre-existing igneous or sedimentary rock underwent high-temperature, high-pressure metamorphism, commonly during Precambrian to Paleozoic mountain-building. Pale irregular zones may represent partial melting or felsic injections.

Uses & applications

Used as crushed stone, aggregate, riprap, and occasionally dimension stone; attractive polished pieces are collected or used decoratively rather than commonly made into jewelry.

Geological facts

The mottled light-and-dark pattern reflects metamorphic segregation of felsic minerals from dark mafic minerals. If the pale material forms true cross-cutting veins, the specimen may be migmatitic gneiss rather than ordinary banded gneiss.

Field identification & locations

Look for compositional banding, flattened or aligned minerals, and a granular texture; granite lacks strong mineral alignment, while amphibolite is typically darker and richer in amphibole. Common in ancient continental shields and metamorphic mountain belts worldwide.