LP GEAR ALN3600LE Upgrade Stylus compatible with and supersedes Audio-Technica ATN3600LE AT3600L cartridge stylus

That stylus is a diamond tip already, it's probably just very worn. It's an older Audio Technica 3600L, which is a conical diamond. it's very cheap and sounds decent for what it is. You can also replace/upgrade it with an LP Gear ALN3600LE elliptical or a Rega Carbon or Carbon Pro.