M - P
Magnetite is an iron ore. As the name suggests, it can be magnetic. Can be. Lodestone is the magnetic variety of the mineral - actively attracting iron filings and paperclips, etc. It's not a very strong magnet, so you aren't going to want to try using it to retrieve carkeys from down a drain or whatever. These pieces are attractive, blob-shaped lumps.
2.5cm, possibly with a few iron filings ABSOULTELY FREE!