The minerals of the olivine group all possess orthorhombie symmety and a structure consisting of independent tetrahedra linked by divalent atoms in octahedral coordination. Minerals of the group show complete diadochy between the atomic pairs Mg and Fe+2 and Mn, i.e. between forsterite, Mn2Si04, and fayalite, Fe2Sio4, and between fayalite and tephroite, Mn2Sio4. The other members of the group a…