Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Dumitras, D.-G. Articles by Hatert, F. Search for Related Content GeoRef GeoRef Citation

APATITE-(CaOH) IN THE FOSSIL BAT GUANO DEPOSIT FROM THE "DRY" CIOCLOVINA CAVE, UREANU MOUNTAINS, ROMANIA

Delia-Georgeta Dumitra¹, tefan Marincea^1,, Essaïd Bilal² and Frédéric Hatert³

¹ Department NII, Geological Institute of Romania, 1 Caransebe Street, Bucharest, RO–012271 omania
² Département GENERIC, Centre SPIN, Ecole Nationale Supérieure des Mines de Saint Etienne, 158, Cours Fauriel, Saint Etienne, Cedex 2, F–42023, France
³ Laboratoire de Minéralogie, Université de Liège, Sart-Tilman, Bâtiment B-18, B–4000 Liège, Belgium

E-mail address: marincea{at}igr.ro

Apatite-(CaOH) is the most abundant phosphate in the deposit of fossil bat guano in the "dry" Cioclovina Cave, ureanu Mountains, South Carpathians, Romania. Initial deposits, of both biogenic and authigenic origin, were chemically equilibrated during diagenesis. Individual crystals are tabular, roughly hexagonal, platy on (0001) and usually between 3 and 15 µm across and up to 1 µm thick. The mean indices of refraction measured for 10 representative samples are 1.645(2) and 1.653(1). The mean measured density [D_m = 3.17(2) g/cm³] is in good agreement with the individual calculated values. The unit-cell parameters calculated as an average of 20 sets of values are a 9.436(13), c 6.868(8) Å. The mineral is Ca-deficient, carbonate- and sulfate-bearing. Less than 2.26% of the phosphate groups are protonated, and less than 4.66% are replaced by sulfate. The cumulative incorporation of other cations in the Ca sites accounts for only 0.71 to 4.07% (mean 2.07%). Both unit-cell parameters and thermal behavior are characteristic for a hydrous A-type carbonated apatite-(CaOH), with molecular H₂O and carbonate substituting for hydroxyl in the structural channels. The multiplicity of the bands in the infrared absorption spectrum (3₃ + 1₁ + 3₄ + 2₂) is consistent with a C₆ point symmetry of the phosphate anion. Whitlockite obtained by thermal breakdown at 1000°C is sulfate-bearing. The authigenesis of the Cioclovina apatite-(CaOH) involved a reaction between calcium carbonate from the moonmilk flows or the cave floor and phosphoric solutions derived from guano, with brushite or an X-ray amorphous phase as a precursor.

Keywords: apatite-(CaOH), physical properties, crystal chemistry, unit-cell parameters, thermal behavior, infrared absorption data, authigenesis, "dry" Cioclovina Cave, Romania.