The ratio / (δ) can also be used to determine paleothermometry in certain types of fossils. The fossils in question have to show progressive growth in the animal or plant that the fossil represents. The fossil material used is generally calcite or aragonite, however oxygen isotope paleothermometry has also been done of phosphatic fossils using SHRIMP. For example, seasonal temperature variations may be determined from a single sea shell from a scallop. As the scallop grows, an extension is seen on the surface of the shell. Each growth band can be measured, and a calculation is used to determine the probable sea water temperature in comparison to each growth. The equation for this is: