Noun 1. thorite - a radioactive mineral consisting of thorium silicate; it is a source of thorium that is found in coarse granite
atomic number 90, thorium, Th - a soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands
mineral - solid homogeneous inorganic substances occurring in nature having a definite chemical composition
The question asks , Radioactive mineral commonly found in the chemical element atomic number 90