Tom, I seem to remember reading something about there being some asbestos in vermiculite. While I hesitate to tell you that using it would mean the same kind of "instant death" that the newspapers attribute to lead and other substances, I would suggest that you get a guarantee that the vermiculite is 100% asbestos free.
For what it's worth, I know of a company that makes automotive brake shoes and pads. They have one customer that specifies that the friction material must have asbestos in it. That customer is--ta-da--the U. S. Government.