An additive to foundry sand molding and core aggregates is used to produce sand cores and molds comprising kyanite, spodumene, titanium dioxide, ilmenite and black iron oxide. The additive produces a sand-based foundry molding and core aggregate which resists the formation of some of the defects commonly associated with the production of castings produced by silica sand-based molding and core aggregates. In particular, the additive improves the quality of castings poured at temperatures higher than those of the pouring temperatures of molten iron, such as in steel castings, and in iron castings with “hot spots.”