Bentonite is a kind of clay. In my job, I've become familiar with it because it is used in drilling mud--the man-made mud that is forced down through drilling tubing and then back up outside of the drilling tubing in order to prevent the well from collapsing (before it is cemented) and to carry the rock cuttings from the drill to the surface. Bentonite is relatively light weight clay, so it is used in the shallow part of an oil or gas well; a heavier mineral, barite, is used when drilling in the deeper, higher-pressure regions.
Now it turns out that bentonite was used as a little piece of misinformation to help build up belief that Iraq was connected to terrorism. After 9/11, the country was attacked again--this time via anthrax sent through the mail to targets in politics and the media. Several people died, and the case remained unsolved until, apparently, very recently. They were in fact about to arrest an American bioweapons scientist, but he conveniently committed suicide before he could be indicted and made to testify.
When the anthrax was mailed, it was accompanied by stereotypical radical Islamist "death to America"-style notes. Obviously people were scared of additional Islamist terror attacks, so few had any trouble believing the notes were authentic.
Glen Greenwald has a somewhat rambling article about this, where he talks about how ABC news reported that the anthrax contained traces of bentonite, which led to a disturbing conclusion.
ABC News, including Peter Jennings, repeatedly claimed that the presence of bentonite in the anthrax was compelling evidence that Iraq was responsible for the attacks, since -- as ABC variously claimed -- bentonite "is a trademark of Iraqi leader Saddam Hussein's biological weapons program" and "only one country, Iraq, has used bentonite to produce biological weapons."ABC was had--there was never bentonite in the anthrax. Indeed, Greenwald suggests that ABC's source at Ft. Detrick, where the anthrax was being tested, could have been the alleged mailer himself, who worked there. Greenwald's question is, who provided this false lead to ABC? ABC is not saying--but if it was Bruce Ivins, it seems as if ABC should say so. Someone wanted this attack linked to Iraq--we citizens should know who it was, and why.
And I'm curious, why would bentonite be used in weaponizing anthrax? I don't know much about it beyond its oil-filed use, except that it is also apparently used in winemaking.