High-pressure synthesis of priderite and members of the lindsleyite-mathiasite and hawthorneite-yimengite series

Experiments investigating simplified members of the alkali-titanate mineral series priderite, lindsleyite-mathiasite (LIMA) and hawthorneite-yimengite (HAWYIM) confirm their stability at pressures between 3.5 and 5 GPa for priderite and LIMA, 4.3 and 5 GPa for HAWYIM at likely mantle solidus temperatures. Starting materials with K/Ba=1 resulted in solid-solutions for LIMA, whereas HAWYIM produced separate hawthorneite (K/Ba approx. 0.5) and nearly pure yimengite (K), indicating the existence of an asymmetric solvus for HAWYIM at high pressures. Priderite was examined with iron present as either Fe³⁺ or Fe²⁺; both are stable at 5 GPa, confirming the possible coexistence of priderite with diamond. X-ray powder diffraction data on end-members synthesized at high pressures and calculated reflection patterns improve the scope of diffraction data on these rare mantle minerals, with only small differences existing between the patterns for the synthetic minerals and those observed or expected for natural minerals.