metamorphic
Likely amphibolite (hornblende-rich metamorphic rock)
Amphibolite, composed chiefly of amphibole (commonly hornblende) and plagioclase feldspar
AI-generated identification · may be incorrectDark green-black, coarse-to-fine crystalline, with a sparkly vitreous-to-silky luster; amphibole hardness is about 5–6 on Mohs, and the rock has no consistent cleavage. The small specimen’s minerals cannot be confirmed from the photo alone.
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Physical properties
Dark green-black, coarse-to-fine crystalline, with a sparkly vitreous-to-silky luster; amphibole hardness is about 5–6 on Mohs, and the rock has no consistent cleavage. The small specimen’s minerals cannot be confirmed from the photo alone.
Formation & geological history
Typically forms when basaltic or gabbroic rocks undergo medium- to high-grade metamorphism; such rocks occur in ancient metamorphic belts of many geological ages.
Uses & applications
Used locally as crushed stone, aggregate, and dimension stone; attractive polished pieces may be collected or used decoratively.
Geological facts
The glittering appearance commonly comes from aligned amphibole crystals, sometimes with mica or other reflective minerals.
Field identification & locations
A dark, dense, crystalline rock with visible elongate or glittering amphibole grains is characteristic; common in metamorphic terrains worldwide. A hand lens and mineral tests would help distinguish it from other dark rocks.
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