Khí-iū-chit chú-iàu iû calcium hydroxyapatite, (Ca5[(PO4)3OH]) chit-chióng chiⁿ-thé lâi cho·-sêng, i nā tú-tio̍h hu̍t chiâⁿ gâu thoat-li̍h chhut hydroxyl group, chôaⁿ piàn-sêng calcium fluoroapatite, ( Ca5[(PO4)3F]). Hydroxyapatitite pí fluorapatitite khah iông-ì iông-kái tī sng.