Olivine can be pure Mg 2 SiO 4 or pure Fe 2 SiO 4 , or a combination of the two, written as (Mg,Fe) 2 SiO 4 . Magnesium and iron can substitute for each other because they both have a charge of +2, an...Olivine can be pure Mg 2 SiO 4 or pure Fe 2 SiO 4 , or a combination of the two, written as (Mg,Fe) 2 SiO 4 . Magnesium and iron can substitute for each other because they both have a charge of +2, and they are similar in size: magnesium cations have a radius of 0.73 Å, and iron cations have a radius of 0.62 Å [1] .
