The Stability of Bredigite and Other Ca‐Mg Silicates

The phase Ca 7 Mg(SiO 4 ) 4 , bredigite, is chemically and structurally distinct from α‐Ca 2 SiO 4 . Experiments on its lower stability limit represent a synthesis limit which is not likely to be an equilibrium boundary. Equilibrium experiments place its upper stability limit at 1372°C and 98 kPa by the reaction image The experimental data also require a second reaction image at the same pressure and temperature and imply that two other reactions relating these phases are located near 1372°C and 98 kPa. Location of these four reactions around an invariant point in P‐T space shows that bredigite is on the low‐pressure side of the reactions.