Olivine is a magnesium-iron-silicate with the formula (Mg, Fe)2SiO4. Olivine is actually a name for a series between two end members, iron-rich fayalite and magnesium-rich forsterite. These two minerals form a series where the iron and magnesium are substituted for each other without much effect on the crystal structure. Olvine is used used in metallurgical processes as a slag conditioner, as well as used as a refractory material to make refractory bricks.