The paper presents the results of analytic investigations of raw materials, silicon and slags of carbothermic process executed by various methods. The analytical techniques: both direct and with sample decomposition have been applied at the Institute of Geochemistry in Irkutsk, Russia to determine the contents of element impurities in quartz raw materials and different types of silicon. These are atomic emission spectrometry (AES), X-ray fluorescence analysis (XRF), AES with concentration and inductively coupled plasma mass spectrometry (ICP-MS). Compared analytical results obtained with different methods agree quite well. At the Department of Metallurgy of Non-Ferrous Metals of Irkutsk State Technical University metallographic investigations carried out using a microscope «Olympus GX-51» in the reflected light. In studying the microstructure of silicon metal the intermetallic inclusions were found which are located along the grain boundaries. Slags analysis showed that they contain silicon, that is the reason for its loss during melting. The article also presents the results of chemical analysis of technical, refined silicon and slag samples, obtained in the laboratory of «Kremniy» CJSC using XRF and chemical gravimetry.