I deliberately didn't specify a size and weight for the spheres, as that is really up to the gamemaster, in my estimation. If I were to drag them out, I would make them around the size of the cliched crystal ball, and about the same weight, or maybe slightly larger than two fists, and around five to ten pounds.
If I get time, next weekend, I hope to write up another non-psionic article (there are two more psionics chapters waiting to be published).