Most consumer grade dry toner is made of magnetite dust (filings gives the impression that the magnetite is much coarser than it actually is), and a carrier which is wax and/or resin. The reason most consumer grade toner has iron in it, is because that allows the stuff to be applied to the to the image drum by brushing 'waves' of it with a magnetic roller assembly.
Non-magnetic dry toner exists, but its more complicated and fussy to get it on the image cylinder. For example, the Midax print engines (Delphax technology based) I used to maintain could use either, but required a different toner delivery assembly. The 'nonmag' toner hopper delivered toner to the image cylinder by blowing air through a sintered metal plate to make the layer of toner above it behave as a fluid. If things weren't Just So (down to things we didn't control very well such as ambient air temperature and humidity, fumes from flexographic ink, etc) it would work poorly if at all. When it did work, we could run the paper web through the press at up to 400 feet per minute or so.