Bachelor thesis deals with mineral exsolutions in rocks. In the first part there is a general description of exsolutions, a definition of cause of dissolution for solid solutions, a description of methods by which exsolutions are studied, and a description of chosen types of mineral exsolutions. This work focuses on exsolutions found in igneous rocks, metamorphic rocks and ultra high pressure metamorfic rocks. The second part contains a discussion about the petrogenetic importance of these processes.