Why igneous wollastonite is so rare in CAIs

Primary wollastonite (wo) thought to have crystallized from a liquid is quite rare in CAIs, having been reported in only two igneous inclusions, White Angel and KT-1 [1, 2]. Both of these CAIs exhibit significant mass fractionations in multiple elements and KT-1 is a FUN inclusion, so it is highly desirable to place as many constraints as possible on their formation. Since phase diagrams previously developed for CAIs do not involve wo [3], we use literature data on wo-saturated and wo-free phase diagrams in the system CaO-MgO-Al_2O_3-SiO_2 (CMAS) to establish a basic framework for describing crystallization of wo-bearing CAIs.