Paramagnetism is generally a reflection of paramagnetic elements such as iron and magnesium.
I'm a fan of using local sources as it reduces transportation costs and I believe is more in line with the ethic of remineralization. However, there are plenty of proponents of rock dust that are willing to transport rock dust great distances because of a certain quality such as paramagnetism. In my view, if rock dust is to be globally accepted, then we need to be using local resources. By green granite, I presume you are referring to a coarse grained dark rock which is probably gabbro. I know of no work on this material, but the same rules for serpentinite apply here.