The crystal substance has been isolated from chloroform-ethanol extract of sea organism Halocynthia aurantium. A set of spectrometry methods was used to describe a structure of this compound. It was appeared that element analysis showed ≈60% chlorine, less silicon, carbon and hydrogen. Another spectroscopy method (UV, IR, NMR) did not give an additional information. The data obtained suggests us that we have the matter with unusual compound. X-ray-phase analysis was used also. On the basis of an element analysis and X-ray diffraction parameters the formula of compound С2H2Si4Cl12 has been offered.