A CO3-bearing member of the hydroxylapatite-hydroxylellestadite series from Tadano, Fukushima Prefecture, Japan: CO3-SO4 substitution in the apatite-ellestadite series

摘要

A CO3-bearing member of the hydroxylapatite-hydroxylellestadite series occurs as a Si-rich part of a hydroxylapatite-hydroxylellestadite series mineral (hydroxylapatite(ss)) in a skarn xenolith from Tadano, Fukushima Prefecture, Japan. Hydroxylapatite(ss) 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 CO3. A representative analysis of the Si-rich part yielded the empirical formula Ca-4.989[(PO4)(1.315)(SiO4)(0.848)(SO4)(0.368)(CO2.943)(0.480)](Sigma 3.011)OH0.629Cl0.264F0.107)(Sigma 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 (SO4, CO3)(2-) + (SiO4)(4-)= 2(PO4)(3)probably occurs in hydroxylapatitess. Therefore, it was concluded that the Si-rich part corresponds to a CO3-bearing hydroxylapatite-hydroxylellestadite series mineral with CO3 partially replacing SO4. Most of the Si-rich part shows CO3 > SO4 and its composition approaches Ca-5(SiO4)(1.5)(CO3, SO4)(1.5)(OH, Cl, F).