Amphibolite
(c) 2006 Andrew Alden, licensed to About.com, Inc. (fair use policy)
Amphibolite is a metamorphic rock composed mostly of amphibole minerals. In practice, it usually is a hornblende schist like this example, because hornblende is the commonest amphibole. Amphibolite forms when basaltic rock is subjected to higher temperatures (550–750°C) and slightly greater pressure range than that which yields greenschist.
For more photos see the Metamorphic Rocks Gallery.
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