Fayalite
Fayalite (Fe2SiO4, commonly abbreviated to Fa) is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system (space group Pbnm) with cell parameters a = 4.82 Å, b = 10.48 Å and c = 6.09 Å. Fayalite forms solid solution series with the magnesium olivine endmember forsterite (Mg2SiO4) and also with the manganese rich olivine endmember tephroite (Mn2SiO4).