To consider the vast P-T space, it is convenient to make subdivisions. This is the precise role of the metamorphic facies, a concept proposed by Eskola at the beginning of the last century. The P-T domain is divided into "metamorphic facies". This is a very practical concept that allows the grouping of rocks with different parageneses, but submitted to given P and T intervals, independently of their chemical composition. The names of these facies are the names of rocks of basaltic composition, metamorphosed in the PT intervals defined for these facies. Thus, amphibolites (of basaltic composition) and sillimanite-metapelites (of clay sediment composition) (the prefix meta indicates that the rock in front of which it is placed is metamorphosed) are classified in the amphibolite facies.  The faciès of the contact metamorphism (or thermal metamorphism) around a plutonic massif are the albite epidote hornfels (Corn AE; cornéenne in french), hornblende hornfels (Corn Hbl), pyroxenes hornfels (Corn Px) and Sanidinite facies. Les faciès BlueSchist, Eclogite, GreenSchist, Amphibolite and Granulite are the facies of regional metamorphism.. A is the anatexis curve.

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