Nineteen kinds of minerals, alone and in bicomponent mixtures with LaC (a mixed ternary complex of trivalent lanthanum stearate and stearin), were added to isotactic polypropylene (iPP). The influences of the minerals on the crystallographic forms of iPP were investigated. A wide-angle X-ray diffraction examination demonstrated that no mineral or LaC acting alone could induce the occurrence of the hexagonal beta-form, whereas the bicomponent mixtures could when the mineral was a calcium compound or contained calcium compounds, whether the calcium compounds had a hexagonal crystallographic form or not. We surmise that the actual beta-iPP substrate in such a system might be some binuclear complexes of calcium and rare earth elements with some specific ligands.