Ferric oxide
The brown gamma iron oxide that was the first practical magnetic layer on tape and floppy disk — the original "normal" tape.
Gamma ferric oxide (γ-Fe₂O₃) is needle-shaped particles dispersed in a binder and coated onto the carrier film. AEG and BASF used iron oxide on Magnetophon tapes as early as the 1930s, and it stayed the standard coating on audio tape, floppy disks, and early computer media for decades. Its low coercivity made it easy to record but limited how densely information could be packed.
The hunt for higher density drove better chemistry: DuPont's chromium dioxide (CrO₂, "chrome tape") in the 1970s raised coercivity, and later came pure metal particles. Ferric oxide became the cheap Type I option, the one still inside the standard cassette long after the pricier tapes existed.