Dielectric properties of natural grown Tourmaline at 100 GHz

CVD diamond is a well known excellent low loss material (tan delta = 0.55. 10(-5)) for microwave transmission e. g. in fusion reactors for the ECRH& CD system. Goal of our investigation is to find out other natural dielectric materials with even low loss tangent properties. Tourmaline is a complex structured natural mineral which grows in large crystals. A disk, sliced perpendicular to the c- axis of the crystal lattice, was used to determine the loss tangent and the dielectric constant in the 100 GHz frequency range.