metamorphic

Tumbled dark metamorphic rock, likely amphibolite

Amphibolite; chiefly hornblende amphibole and plagioclase feldspar, with possible biotite and epidote

AI-generated identification · may be incorrect

Dark gray-green, fine- to medium-grained, weakly foliated, with a dull to slightly vitreous luster; typical hardness is about 5.5–6.5 Mohs and specific gravity 2.9–3.3. The rounded shape indicates natural water wear or tumbling.

Identified September 9, 2026More metamorphic →

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At a glance

Common name: Tumbled dark metamorphic rock, likely amphibolite
Scientific name: Amphibolite; chiefly hornblende amphibole and plagioclase feldspar, with possible biotite and epidote
Category: metamorphic
Identified: September 9, 2026
Method: Standard

AI Estimated Value

$1–$10 as a common tumbled or collected specimen; approximately $10–$30 for an attractive polished piece.

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

Forms when basalt or gabbro undergoes medium- to high-grade regional metamorphism, commonly during mountain building; many examples are Precambrian to Paleozoic, though amphibolite forms throughout geologic time.

Uses & applications

Used as crushed aggregate, road stone, riprap, and occasionally as a durable ornamental or lapidary stone; generally modest value as a polished pebble.

Geological facts

Amphibolite’s dark color and amphibole-rich composition distinguish it from lighter gneiss and quartz-rich rocks. Foliation may appear as subtle aligned streaks or elongated mineral grains.

Field identification & locations

Look for dense, dark greenish-gray material with visible interlocking grains and little reaction to dilute acid; amphibole commonly forms splintery dark crystals. Common in metamorphic belts worldwide, including Canada, Scandinavia, the Appalachians, and Precambrian shields.