metamorphic

Likely amphibolite (hornblende gneiss or mafic metamorphic rock)

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

AI-generated identification · may be incorrect

Dark gray-green, coarse crystalline, and weakly foliated, with a dull to slightly glassy luster; typical hardness is about 5–6 Mohs and specific gravity 2.9–3.3. The image suggests interlocking amphibole and pale feldspar grains, though exact identification requires a fresh surface or testing.

Identified September 13, 2026More metamorphic →

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At a glance

Common name: Likely amphibolite (hornblende gneiss or mafic metamorphic rock)
Scientific name: Amphibolite, chiefly hornblende amphibole and plagioclase feldspar, with possible quartz, biotite, or epidote
Category: metamorphic
Identified: September 13, 2026
Method: Standard

AI Estimated Value

About $1–$10 for a common hand specimen; attractive polished or well-crystallized pieces may sell for $20–$75.

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 basalt or gabbro undergoes medium- to high-grade regional metamorphism, commonly during mountain building; ages range from Precambrian to recent metamorphic belts. Common in metamorphic terranes worldwide, including Scandinavia, Canada, the Appalachians, and parts of Africa and India.

Uses & applications

Used as crushed stone, road aggregate, riprap, railroad ballast, and occasionally dimension stone or decorative landscaping material; generally not a jewelry stone.

Geological facts

Field identification relies on its dense dark-green/black appearance, granular texture, and abundant elongated hornblende crystals; it is typically harder and heavier than ordinary basalt. A streak, hardness, and thin-section test can distinguish it from gabbro, diorite, or serpentinite.

Field identification & locations

Commonly found in metamorphic belts and near ancient mafic intrusions or volcanic rocks; look for foliation and amphibole needles, with little reaction to dilute acid. Avoid calling it definitive without petrographic or mineralogical testing.