metamorphic
Amphibolite (likely)
Amphibolite, composed mainly of hornblende-group amphibole and plagioclase feldspar
AI-generated identification · may be incorrectDark gray-green, coarse-speckled, and weakly foliated; amphibole has Mohs hardness 5–6 and plagioclase 6–6.5. The rounded shape suggests a water-worn pebble; the photo alone cannot confirm the mineralogy.
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Physical properties
Dark gray-green, coarse-speckled, and weakly foliated; amphibole has Mohs hardness 5–6 and plagioclase 6–6.5. The rounded shape suggests a water-worn pebble; the photo alone cannot confirm the mineralogy.
Formation & geological history
Forms when basaltic or gabbroic rock is metamorphosed, commonly under medium- to high-grade conditions; specimens may range from Precambrian to much younger.
Uses & applications
Used as crushed stone and dimension stone; attractive polished pieces are collected or used decoratively.
Geological facts
Amphibolite’s dark amphibole grains may appear elongated or aligned, while lighter feldspar forms contrasting flecks.
Field identification & locations
Common in metamorphic belts worldwide. Look for a dense dark rock with visible dark amphibole and lighter feldspar; confirm by examining fresh surfaces or testing minerals, since several dark rocks look similar.
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