The main formations of the Mihaliççik region are ultramafites, "eclogites", basic volcanics, greenschists and various rocks of the "blue schist" faciès. The ultramafite group consists of dunites, wehrlites, serpentinites and pyroxenites. The age of the consolidation of these rocks seems to be Paleozoic (K/Ar age of 306 Ma.). However the final emplacement of these bodies was later; they were emplaced as "cold intrusions" during the alpine orogenesis. The "eclogites" are tectonic inclusions brought up by the serpentinites. Rocks of the "blue schist" facies are due to the metamorphism under high pressure and low temperature of a geosynclinal sequence of basic volcanics, tuffs, graywackes, radiolarian cherts and limestones. Rodingites are frequently found in the most deformed and serpentinized parts of the ultramafic intrusion. These rocks were primitively diabases and gabbros which underwent calcic metasomatism during the serpentinization as a result of the transformation of the pyroxene into serpentine minerals. The Mihaliççik region has been submitted to two different metamorphic events: a) An epizonal metamorphism of Paleozoic age which produced, for instance, graphitic schists. b) A younger metamorphism, very probably of alpine age, resulting in the formation of greenschists and glaucophane schists. The younger metamorphic event may be subdivided into two phases. At the beginning (main phase), when the pressure was high and the temperature low, rocks of the "blue schist" facies were formed: according to mineral associations it is possible to distinguish three zones of progressive metamorphism. Later on, a temperature increase led to the formation of greenschists. The formation of the glaucophane schists of the Mihaliççik region results from an isochemical metamorphism, with no addition of sodium of external origin. The main factors of this metamorphism were physical and related probably to the rapid subsidence of a geosynclinal sequence in which the geothermal gradient was unusually small. The return to a normal geothermal gradient led to the temperature increase of the last phase of metamorphism.