To all of you contributing to this thread: This has been a VERY interesting and informative exchange,with plenty of new material thrown in,and I appreciate the spirit and cooperativeness of all !
There were much earlier threads about the exact nature of the materials used.Someone-quite a while ago-suggested the materials were made with a very up-to-date technology.
Cabosil (silocaine) was mentioned.This stuff is available "over the counter" for about $ 5.95 pound,and is used in fireworks and (prepared a bit differently) in pharmaceutical products,electronics,and certain paints.
When made "perfectly" in a proper spray dryer (a recent and notable Swiss upgrade of the Russo-Iraqi method),it was actually unsuitable for mailing,because you couldn't get it to hold still long enough to put it into an envelope.
The Russians (and their "clients") used to use a spray dryer to prepare their bioweapons.Instead of using cabosil,they used diatomaceous earth and Bentonite (a water resistant clay)-plus a third,undisclosed material which helped eliminate clumping.It was almost exactly the way we used to make it,before we stopped production in 1972: no surprise,because the Russians had penetrated our program so thoroughly,they were reading copies of our internal reports before the ink was dry on the originals.
I concur. Thank you, Gene, and every-body else on this thread.