Monticellite and kirschsteinite (commonly also spelled kirschteinite[3]) are gray silicate minerals of the olivine group with compositions CaMgSiO4 and CaFeSiO4, respectively.

Most monticellites have the pure magnesium end-member composition but rare ferroan monticellites and magnesio-kirschsteinite are found with between 30 and 75 mol.% of the iron end member.

Monticellite is named after Teodoro Monticelli, an Italian mineralogist (1759–1845).

Kirschsteinite is named after Egon Kirschstein, a German geologist.

The unit cell is somewhat larger than for the calcium free olivines forsterite and fayalite with and for monticellite