Diamonds are the hardest known minerals on the earth. I can only think of one thing that can scratch a diamond, and that's a material called "ultra hard fullerite." It's been shown to scratch diamonds using an atomic force microscope.

Diamond is the hardest mineral we know of--so I don't think you'll be able to find a mineral that will scratch it. The hardness of a mineral is determined by whether it can scratch another mineral, so diamonds are at the top of the scale (called Moh's Hardness scale; it goes from 1-10).