To meet the requirement of a process description with focus on silica impurity distribution on material streams of a seawater magnesia production plant of RHI Normag AS in Norway, a detailed investigation was performed. Aside from the preparation of a material balance for silica bearing mineral phases, proposals for their removal with respect to magnesia losses should be given. A sampling campaign covering one week of production provided the data base. Samples of slurries and solids were transported to Leoben, further processed at the Chair of Mineral Processing (Montanuniversität Leoben) and prepared for chemical and mineralogical analysis. Based on the assays and the accompanying mineralogical investigation, a chemical mineralogical phase model of every material stream as well as a material balance was created. Further processing steps were carried out to characterize the separation efficiency and show up enrichments of impurities in the feed of purification steps. With the finished balance it was possible to follow the way of silicate bearing mineral phases through the process. Together with the characterisation of the purification efficiency and SiO2 distribution on size classes in the feed streams, using the Henry Reinhardt charts, the results of the thesis describe the prevailing process conditions at the time of sampling and serve as basis for further optimization.