A supplier of small quantities in CA is Hill Brothers. This company should be huge, but unfortunately, in the early days, one of the favoured ways of strengthening and lowering the cost of magnesite was to add asbestos. The law suits have palgued the company IMHO.

It is beautiful to cast with - I have made very convincing black onyx and lapis lazuli that would fool jewellers - because it is as hard as natural stone and does not burn under the torch.

IT is really hard, completely fireproof, and more expensive than gypsum plaster. What i do is "dilute" the cement with extremely fine bubbles generated by CO2 gas, to form a very stable and weatherproof carving stone. Weights can vary to harder than granite, to soft as styrofoam.