metamorphic

Hornblende-bearing metamorphic rock (probable amphibolite)

Amphibolite; chiefly hornblende amphibole and plagioclase feldspar

AI-generated identification · may be incorrect

Dark gray-green, coarse-grained, weakly foliated, with vitreous to dull luster; hornblende hardness 5–6 and plagioclase 6–6.5 Mohs. Crystals appear interlocking rather than sharply formed, with no obvious cleavage visible at this scale.

Identified September 8, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when basaltic or gabbroic protoliths undergo medium- to high-grade regional metamorphism, commonly during mountain building. Its age depends on locality and may range from Precambrian to recent tectonic events.

Uses & applications

Used locally as crushed aggregate, road stone, and occasionally dimension stone; small unattractive pieces generally have little jewelry value.

Geological facts

Amphibolite is identified by abundant dark amphibole surrounding lighter feldspar, often recording ancient oceanic crust or mafic intrusions transformed by heat and pressure.

Field identification & locations

Common in metamorphic belts worldwide, including the Appalachians, Canadian Shield, Scandinavia, and many mountain ranges. A streak, fresh fracture, and thin-section or mineral test would distinguish it from hornblende granite or gneiss.