there are 252 nuclides in nature that have never been observed to decay. they occur among the 80 different elements that have one or more stable isotopes. see stable nuclide and primordial nuclide. unstable nuclides are radioactive and are called radionuclides. their decay products ('daughter' products) are called radiogenic nuclides. 252 stable and about 87 unstable (radioactive) nuclides exist naturally on earth, for a total of about 339 naturally occurring nuclides on earth.