original: Natural ytterbium is a mix of seven stable isotopes.
simplifications: Natural ytterbium is made of seven stable isotopes. Ytterbium is a mix of seven stable isotopes. Natural ytterbium is made of seven isotopes. Natural ytterbium contains seven stable stable isotopes. Ytterbium is a mix of seven stable isotopes. Seven stable isotopes mix to form natural ytterbium. Natural ytterbium is a mix of seven variations of the element. Natural ytterbium is made of seven stable isotopes. Natural ytterbium is made from a mix of seven stable isotopes. Natural ytterbium is a mix of 7 solid isotopes.