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CO (sub 3) substitution in apatite; further insight from new crystal chemical data of Kasekere (Uganda) apatite

Paola Comodi and Liu Yu
CO (sub 3) substitution in apatite; further insight from new crystal chemical data of Kasekere (Uganda) apatite
European Journal of Mineralogy (October 2000) 12 (5): 965-974

Abstract

The vibrational and structural characteristics of a CO (sub 3) -rich apatite from an extrusive carbonatite in Kasekere, Uganda, were studied by infrared and Raman spectroscopy, single-crystal X-ray diffraction and electron microprobe analysis. Electron microprobe analysis provided, based on Sigma (large cations) = 10, a cation content of (Ca (sub 9.78) Sr (sub 0.05) Fe (sub 0.01) REE (sub 0.09) Na (sub 0.07) ) (P (sub 4.38) Si (sub 0.52) S (sub 0.04) ) and an anion content of (F (sub 0.54) Cl (sub 0.03) ). According to the structural refinement, the channel's anion occupancy is reduced, and the OH-content is about 1.2. The resulting Sigma (P+Si+S)<6 indicates that carbonate anions enter the tetrahedra. The IR spectrum exhibits all the bands of PO (sub 4) , the V (sub 3) and V (sub 4) modes of SiO (sub 4) as well as the V (sub 2) and V (sub 3) modes of the carbonate group. In addition the structural refinement is compatible with a partial replacement of PO (sub 4) by CO (sub 3) and also the broadening of the Raman V (sub 1) band of PO (sub 4) (15 cm (super -1) in Kasekere vs 5 cm (super -1) in F-apatite) correlates with a replacement of PO (sub 4) by CO (sub 3) . The lateral dimensions of the structural channel (Ca2-Ca2 = 4.105(2) Aa vs 4.084(2)Aa in pure OH-apatite) point to the presence of CO (sub 3) in the channels as well. Moreover in the infrared spectra, the curve fitting technique did show a wide band at 1525 cm (super -1) , implying an A-site carbonate in a B-type dominant carbonate Ap. Comparison of multimethod analyses suggests that the Kasekere apatite is the first occurrence of apatite from a natural environment in which, in addition to a larger substitution of CO (sub 3) for PO (sub 4) , few percents of CO (sub 3) enter the channel. Tentatively, the formula is: (Ca (sub 9.78) Sr (sub 0.05) Fe (sub 0.01) REE (sub 0.09) Na (sub 0.07) ) (P (sub 4.38) Si (sub 0.52) S (sub 0.04) C (sub 1.23) ) O (sub 23.45) (F (sub 0.54) OH (sub 1.2) Cl (sub 0.03) (CO (sub 3) ) (sub 0.23) ).


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 12
Serial Issue: 5
Title: CO (sub 3) substitution in apatite; further insight from new crystal chemical data of Kasekere (Uganda) apatite
Author(s): Comodi, PaolaLiu Yu
Affiliation: Piazza Universita, Dipartimento di Scienze della Terra, Perugia, Italy
Pages: 965-974
Published: 200010
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 27
Accession Number: 2001-000771
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
S02°00'00" - N04°00'00", E29°00'00" - E35°00'00"
Secondary Affiliation: Wuhan Institute of Chemical Technology, CHN, China
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute.
Update Code: 200101
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