The term large-ion lithophile element (or LILE) is frequently used, but poorly defined in the geochemical literature. Some authors use LILE as a synonym for incompatible (or hygromagmatophile) trace elements (e.g.), whereas others use LILE to refer to a specific subset of incompatible trace elements characterized by small charge to ionic radius ratio (or low field strength elements; ). relative to more compatible trace elements. The LILE are strongly enriched in the upper continental crust (. ), but occur in lower concentrations in the deep continental crust due to its overall more mafic character and selective loss of some LILE during high-grade metamorphism (see Metamorphism).