IntroductionDividing the PT space of metamorphism into several subdivisions independent of the composition of the metamorphosed rock would enormously facilitate communication between petrologists regarding the degree of metamorphism. In 1915, Eskola introduced the concept of metamorphic facies to achieve such a classification. Eskola emphasized mineral assemblages (in mafic rocks) rather than index minerals. A facies can be defined as: “A group of mineral assemblages, each developing a specific chemical composition in the rock, and is characteristic of the P and T under which the rocks have metamorphosed”. Therefore, if the overall composition of the rock and the P and T at which it crystallized are known, then prediction of the mineral assemblage can occur. The facies initially defined by Eskota were green schist, corneal pyroxene, amphibolite, granulite, sanidinite, glaucophene schist (blue schist) and eclogite facies (Fig. 1). In the eclogite facies, metabasaltic rocks contain the characteristic omphacitic pyroxene + almandine-pyrope-grossular assemblage. garnet, creating dense and beautiful green and red rocks (Table 1). Plagioclase is not present in eclogite facies rocks due to its stability. Accessory minerals are kyanite, quartz, rutile, orthopyroxene and coesite which are high pressure rocks. formed in a wide range of temperatures (temperatures above 600 0 C in Figure 1). Figure 1: Pressure-temperature diagram showing the fields of different metamorphic facies. The transition from blueschist facies to eclogite facies involves the reaction of glaucophane and paragonite to form garnet -omphacite assembly: Gln + Pg = Prp + Jd+ Qtz + H2Oat pressures greater than 1.2 GPa. But glaucophene alone can remain stable in the eclogite facies. What minerals/reactions demonstrate their distinctive formation conditions? ​​Eclogites are very dense rocks with a density consistently greater than some ultramafic mantle rocks and, due to the high density of eclogites, their origin can be easily linked to very high pressure conditions during formation. Eclogites occur in very different geodynamic contexts. Low temperature eclogites (glaucophane + paragonite = garnet + omphacite) can result from subduction of oceanic lithosphere and form from blue shales (high pressure, low temperature eclogites), one such example is the Alps. Intermediate eclogites may result from the stacking of continental crust from amphibolites (mid-temperature eclogites). At high temperatures, hydrates are absent from eclogite and kyanite is often a characteristic additional mineral in addition to Grt + Omp. High-temperature eclogites form in collisional or extensional settings where the geothermal is abnormally "hot" due to magmatic heat transfer from the mantle..