The topic of my work are atoll or multiple-grown garnets from various environments, mainly from eclogite facies rocks. I mainly focus on mass balance of main and trace elements during decomposition of garnet core and subsequent incorporation of released elements in formation of new phases. Furthermore, I focus on description of the phase and texture relations in metamorphic minerals and thermodynamic modeling of temperature-pressure conditions of metamorphic rocks. The results will help to understand the mechanism, when the rocks are subject of reactions by fluid or minerals are partly decomposed during temperature-pressure changes.