metamorphic

Banded metamorphic rock, likely gneiss or amphibolite

Composition uncertain; probable quartz–feldspar–amphibole assemblage

AI-generated identification · may be incorrect

Dark gray, greenish-black, and pale bands with a dull to slightly satin luster; appears fine- to medium-grained and rounded/polished. Estimated hardness is about 5–7 Mohs; crystal structure and cleavage cannot be confirmed from the image.

Identified September 7, 2026More metamorphic →

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Physical properties

Formation & geological history

Likely formed when a pre-existing igneous or sedimentary rock underwent regional metamorphism at moderate to high temperature and pressure, commonly during mountain building. Geological age cannot be determined visually.

Uses & applications

Useful mainly as a decorative or collecting specimen; comparable gneiss and amphibolite are used as crushed stone, aggregate, dimension stone, and occasionally for countertops.

Geological facts

The contrasting bands likely reflect compositional layering, with darker amphibole- or biotite-rich material and lighter quartz- or feldspar-rich material. Exact identification requires a fresh surface, grain inspection, and mineral tests.

Field identification & locations

Look for alternating mineral bands, interlocking grains, and absence of vesicles or sedimentary layering. Common sources include metamorphic belts worldwide, especially the Canadian Shield, Scandinavia, India, and the Alps.