olivine n 1: a mineral consisting of magnesium iron silicate; a source of magnesium
Olivine \Ol"i*vine\, n. [Cf. F. olivine.] (Min.) A common name of the yellowish green mineral chrysolite, esp. the variety found in eruptive rocks. It is a silicate of magnesium and iron ({(Mg,Fe)SiO4}). [1913 Webster +PJC]
Chrysolite \Chrys"o*lite\, n. [L. chrysolithos, Gr. ?; chryso`s gold + ? stone: cf. F. chrysolithe.] (Min.) A mineral, composed of silica, magnesia, and iron, of a yellow to green color. It is common in certain volcanic rocks; -- called also {olivine} and {peridot}. Sometimes used as a gem. The name was also early used for yellow varieties of tourmaline and topaz. [1913 Webster]