Commonly applied ordinary ceramic refractory materials are usually based on oxidic components such as alumina, silica or magnesia. For certain applications nonoxides like AlN, SiC or carbon are used in addition to enhance the properties. As the existence of several other phases in the Mg-Al-Si-O-C-N system is proofed, their possible application in refractories is of great interest. This concerns shaped materials and also unshaped mixes. It is known that in unshaped carbon containing refractory mixes that contain elements with high affinity to oxygen (e.g. Al), complex phase systems develop during use. It is also expected that the application of different additives acting as antioxidants in Al2O3-C and MgO-C shaped refractories leads to a varied phase development. So far there was a lack of knowledge which phase combinations might arise and how the formation depends on the fabrication and application conditions (starting materials, atmosphere and temperature). Thermochemical calculations were performed showing that under the conditions of the planned experiments usually only oxides should be stable. Sintering experiments within the Mg-Al-Si-O-C-N system showed something different. Several sintering conditions were investigated to find out the influence of the used starting materials, the furnace atmosphere, the sintering temperature and the dwell time at maximum temperature on the phase formation. The main compounds that were formed under the here examined conditions were Al4O4C, Al4C3, Al28O21C6N6, Al3OCN, Al4SiC4, Al8SiC7, AlN and SiC among some miner amounts of AlONs, the solid solution (Al2OC)1-x(AlN)x or polytypes. Summing up, the formation of a large variety of compounds within the matrix of the here investigated materials was confirmed. The determination of the influence of these phase combinations on the mechanical, physical and chemical properties of the material was not the main target of this thesis. The performed investigations reveal the most important phase relations within the Mg-Al-Si-O-C-N system. Depending on the fabrication or application conditions certain phase combinations arise. As a conclusion the phase formation can be influenced by adjusting production parameters and be shifted towards a desired one that could enhance the properties of refractory materials produced thereof.