 Natural ytterbium is a mixture of seven stable isotopes , which altogether are present at concentrations of 3 parts per million . This element is mined in China , the United States , Brazil , and India in form of the minerals monazite , euxenite , and xenotime . The ytterbium concentration is low , because the element is found among many other rare earth elements ; moreover , it is among the least abundant ones . Once extracted and prepared , ytterbium is somewhat hazardous as an eye and skin irritant . The metal is a fire and explosion hazard . 
