Amphibolite forms when basaltic rock is subjected to higher temperatures (550–750°C) and slightly greater pressure range than that which yields greenschist. Amphibolite is also the name of a metamorphic facies—a set of minerals that typically forms at a specific range of temperature and pressure.
For more photos see the Metamorphic Rocks Gallery.
Other galleries:
Fossils
Geologic Features and Processes
Glaciers and Ice
Landforms
Minerals
Rocks
Geology and Society