Amphibolite

A dark metamorphic rock made mostly of hornblende and plagioclase.

Amphibolite specimen — Photo: Karelj, CC BY-SA 3.0, via Wikimedia Commons

How to identify amphibolite

Black to dark green, sparkly with hornblende.
Elongated crystals often aligned.
Heavy.

Often confused with

Gabbro
Gabbro has blocky pyroxene and random texture.
Compare side by side
Gneiss
Gneiss has light and dark banding.
Compare side by side

Where it's found

Adirondack Mountains, New York
Scottish Highlands
Swiss Alps

Uses

Crushed stone and dimension stone.

Rock tumbling

Great for tumbling.

Did you know?

Most amphibolites started out as basalt or gabbro.

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