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An amphibolite is a rock composed mainly of one of the amphibole group minerals. It is typically dark-colored and heavy, with a foliated or schistose structure.

Although the rock-type is found in both unmodified igneous versions and as metamorphic rocks, traditionally only the metamorphosed form was called amphibolite. In modern sources this distinction is reduced and the name is sometimes applied to rocks of both origins.

The 1911 Encyclopaedia Britannica contains a substantial entry for amphibolite. There are some pros and cons to using a one-hundred year old reference. An important aspect for non-professionals is, technical articles like this at the turn of the century were written to be meaningful without advanced equipment which the average person will not have. To read the 1911 entry, see Amphibolite (1911 Encyclopaedia Britannica).