incompatible element
英[ˌɪnkəmˈpætəbəl ˈelimənt]美[ˌɪnkəmˈpætəbəl ˈɛləmənt]
In petrology and geochemistry, an incompatible element is an element that is unsuitable in size and/or charge to the cation sites of the minerals, and is defined by the partition coefficient between rock-forming minerals and melt being much smaller than 1.