Quite a new idea, you can try and share the experience.Have anyone tried using Silicon carbide (SiC) instead of (or mixed with) granite or quartz?
SiC has a Youngs modulus of >400GPa, significantly higher than granite or quartz. Will this result in a higher modulus for the finished casting?
SiC is available in 1200 to 8 mesh, roughly 5µm to 5mm. It's used for grinding stone and glass as well as for sandblasting so should not be hard to find in most places, except possibly the very fine and very course grades, but not as cheap as sand.
It's extremely hard, which I think is mostly an advantage. But it may cause some problems such as abrasion of mold release and difficulty of processing after casting?