A CO 3 -bearing member of the hydroxylapatite–hydroxylellestadite series from Tadano, Fukushima Prefecture, Japan: CO 3 -SO 4 substitution in the apatite–ellestadite series

Abstract

A CO -bearing member of the hydroxylapatite–hydroxylellestadite series occurs as a Si-rich part of a hydroxylapatite–hydroxylellestadite series mineral (hydroxylapatitess) in a skarn xenolith from Tadano, Fukushima Prefecture, Japan. Hydroxylapatitess is composed of Si-poor and Si-rich parts. The Si-poor part is F-rich hydroxylapatite. The infrared spectrum of the Si-rich part demonstrates the presence of B-type CO 3 . A representative analysis of the Si-rich part yielded the empirical formula Ca 4.989 [(PO 4 ) 1.315 (SiO 4 ) 0.848 (SO 4 ) 0.368 (CO 2.943 ) 0.480 ] ∑3.011 (OH 0.629 Cl 0.264 F 0.107 ) ∑1.000 on the basis of 8 cations, assuming Si = S + C. There is a very strong inverse correlation between Si and P in both the Si-poor and Si-rich parts. These data indicate that the substitution mechanism (SO 4 ,CO 3 ) 2– + (SiO 4 ) 4– = 2(PO 4 ) 3– probably occurs in hydroxylapatite ss. Therefore, it was concluded that the Si-rich part corresponds to a CO 3 -bearing hydroxylapatite–hydroxylellestadite series mineral with CO 3 partially replacing SO4. Most of the Si-rich part shows CO 3 > SO 4 and its composition approaches Ca 5 (SiO 4 ) 1.5 (CO 3 ,SO 4 ) 1.5 (OH,Cl,F).