[yqkjnggp] Scratching with a diamond

The cool thing you can do with a diamond is scratch rubies and sapphires and tungsten carbide and everything else with it, including other diamonds.

(I think every other notable quality of a diamond is significantly exceeded in that quality by some other material.)

Create diamond jewelry in a form factor that facilitates scratching things with the diamond.

Stylus, or converts into a stylus: screw on a body.  Maybe pendant.

The diamond should have a cut that sharpens to a point, maybe the brilliant cut upside down.

Unfortunately, rubies and sapphires tend to be very small so may be awkward to scratch.  The diamond probably needs to be part of a precise tool, and the ruby or sapphire needs to be held very securely.  You will probably also need magnification to see the scratches on the softer material.

The other cool thing you can do with a diamond is see it resist being scratched by everything else.  The flat top of the brilliant cut might be good for this.  As before, there are numerous practical difficulties in demonstrating scratch resistance.

Perhaps yet another cool thing you can do best with a diamond is use it to apply high pressure: diamond anvil cell.  It's not so easy to tell that diamond is best, though.