Starting at the most basic of theoretical questions, is it chemically possible for these minerals to be deposited by an organic enzyme? I'm particularly interested in diamond because it's pure carbon, which is very plentiful in the environment. Perhaps, for example, one enzyme might set down methane molecules together to form a sort of seed crystal, then another enzyme might continue the process by stripping of a hydrogen atom and depositing methyl group in its place until the crystal grows to the right size. In short, is the energy required to form these diamond bonds too high for an organic enzyme to make?
Then, assuming that's possible, would a skeleton that uses diamonds have any significant advantage in terms of strength over the normal hydroxylapatite bones (assume the crystals are roughly the same size). Lastly, if diamond is a particularly poor choice for this application for whatever reason, would other gem grade minerals (e.g. quartz, corundum, beryl, etc.) function better?
In terms of the rest of this particular creature's anatomy, it's basically a human that's been augmented by magic. The magic has made all of its body systems as efficient as possible, in effect replacing the "good enough to breed" standard of evolution with "as close to perfect as humanly possible". However, I want to avoid using magic to make its body function on a day-to-day basis.