The atom is the smallest possible "mineral", because it, by definition, is an element. Anything underneath that (e.g. quarks, pions, leptons, gluons, neutrinos, photons, etc.) is abstract.

So where's the distinction between mineral and animal? Animals are made of atoms. And we count parts of animals, such as a leather jacket, as animal for these purposes. So a fragment of bone would count as animal, even though it's just a big pile of calcium atoms. So what about a single atom removed from that bone? Is that animal, while an identical atom removed from a rock is mineral? If we say that both atoms are mineral, then the difference between animal and mineral must lie in the form rather than the matter. But then a dinosaur bone has animal form but is made of mineral matter that was never part of the animal. Chalk is clearly a mineral but is made of what was once animals. In fact, given the existence of the "rock cycle", in which volcanic, metamorphic, and sedimentary rocks all turn into each other - and into animals and plants and back again - with slow but ineluctable regularity, it seems that there is no objective dividing line between any of our three categories, and it's all just arbitrary.

[Breadmaster] It's only a game!

Going back a bit, I did apply to load the revolver in that Derren Brown thing. I got as far as having to do an audition tape but it never went further. Probably I was just too strange.

[BM] If it is alive/dead but the components thereof have not sufficiently decomposed to the point where it would be considered a mineral by geological standards, then it's animal and/or vegetable. A cricket ball, e.g. is both animal and vegetable. Bone, if that were the object in question, I would list as animal and mineral.

Or they just found the idea of Darren and Derren on stage at the same time to be too disturbing...

[BM] All sounds a bit quantum, to me.
What you're trying to do is draw definite lines along fuzzy boundaries, which looks OK from a distance but when you look closely, well, aren't.