ˈ ̷ ̷ˌ ̷ ̷ ̷ ̷ noun
: a pure chemical compound in some cases hypothetical but regarded as a component entering into solid solution with other pure chemical compounds to form an isomorphous series of minerals
fayalite Fe 2 SiO 4 and forsterite Mg 2 SiO 4 are end-members of the olivine series (Mg,Fe) 2 SiO 4