(Mg,Fe)SiO4

from The Collaborative International Dictionary of English v.0.48

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]