Phase Relation in the System Ca₃(PO₄)₂-MgSiO₃

Abstract

Phase relations in the system tricalcium phosphate (3CaO⋅P2O5=C3P)-enstatite (MgO⋅SiO2=MS) have been investigated in the temperature range 1100 to 1600°C by means of the quenching method. C3P takes β-type (whitrockite) in a wide region by dissolution of MgO, and diopside (d) appeared in the composition range more than 40mass% C3P by a reach in between MgSiO3 and liberated CaO. The enstatite transfers to iron-free pigeonite (pi) by taking CaO in an MS-rich region, where pi coexists with protoenstatite, MgSiO3 (pr). Primary crystals which appeared in a wide region are β-C3P and pi, and primary diopside appears in a narrow region at a minimum temperature (1265-1305°C). In the subsolidus region below 1245°C, β-C3P coexists with d, pi or pi-pr mixture. The system is not binary and it should be discussed from the ternary system C3P-M-S and the quaternary system C3P-CMS2-MS-S.