Sulfur in natural materials can vary widely in isotopic composition: compilations of the δS values of natural sulfur-containing materials include values ranging from −55‰ to 135‰ VCDT. The ranges of δS values vary across sulfur-containing materials: for example, the sulfur in animal tissue ranges from ~ −10 to +20‰ VCDT, while the sulfate in natural waters ranges from ~ −20 to +135‰ VCDT. The range of sulfur isotope abundances in different natural materials results from the isotope fractionation associated with natural processes like the formation and modification of those materials, discussed in the next section.