Free Magic elementals are beings of Free Magic that are, in some way, associated with one or several elements. Only two specific types of elemental are named in the Old Kingdom series: Ferenk and Stilken. It is not revealed what elements the Stilken is composed of, whereas the Disreputable Dog comments that Ferenks are beings of stone and mud. True to this description, the Ferenk that Lirael and Sam encountered in Abhorsen seemed to live underground.
It is possible that most Free Magic elementals dissipated into their elements when the Charter was created. See information on Ferenk.