Do you know any important uses for Olivine (Forsterite)?

Answer 1

Actually olivine occurs as a complete solid solution between the end members fayalite and forsterite. To actually find a pure end-member is pretty rare. It's a magnesium, iron silicate with varying amounts of mg and iron substituting into the crystal structure. The most common use for it is as the gemstone peridot but it is used some as an abrasive and as an ore for magnesium.

Answer 2

The gemstone Peridot is gem quality Olivine.
Olivine is also mined as refractory sand for the casting industry and for the manufacture of refractory bricks.