Vermiculite has become a lot harder to find, and less desirable generally, because some of it was shown to include asbestos. The Libby mine in Montana was shown to contain asbestos, something Libby was well aware of. The production of the Libby mine was widely marketed for a variety of uses and a large proportion of the vermiculite marketed in the US sold before the mid-90s is assumed to be contaminated.

http://www.epa.gov/asbestos/pubs/verm.html

http://en.wikipedia.org/wiki/Vermiculite

Later mining has undertaken a testing program to make sure the vermiculite is free of asbestos. It has to be noted that these programs are largely operated by the companies doing the mining. The effectiveness of the testing is being reviewed.

The bottom line is vermiculite has lost market share as people have shifted to alternatives.

The alternative offered, even as it is admitted to have different physical quality, is Pearlite.