[Enamel]

Hello everyone.

I have one simple question about the fluorapatite. I've read on the internet, and I've been told in school, that the formula for fluorapatite is:

Ca5 (PO4)3 F

However, I've also read/been told that the formula is:

Ca10 (PO4)6 F2

The same thing goes for the hydroxylapatite (where there is an OH- instead of F-). I'm not in a chemistry-specific program (dental school actually), so I don't really know much about chemistry myself. I'm curious to know which formula is the correct one: the "bare minimum" one or the one where every element/molecule is doubled? I'm particularly interested in knowing which one is the actual one found in the tooth enamel. My guess is that the "theoretical" formula is simply the "basic" one (Ca5, etc), but in the real world the fluorapatite will bind with another fluorapatite for stability reason, but that's just a random guess. Can anyone shed some light?

Thanks.

[Borek]

I would go with the simpler one.

My guess is that the Ca₁₀ formula can reflect the content of the unit cell, while the Ca₅ formula is just the most basic one. But I have no idea what the crystal structure is, perhaps someone else will be able to chime in.