Hand Tools Archive
Oh, interesting, I thought I had the correct MSDS sheet for it earlier, but apparently not. The one I pointed to before said it was 70-80% aluminum oxide.
But it turns out there are SDS sheets on the McMaster site for the compounds. This one says that it's 70-90% iron oxide, and that's it (for abrasives).
So the one I found earlier must be the wrong one.