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A re-investigation of ardealite from the type locality, the "dry" Cioclovina Cave (Sureanu Mountains, Romania)

Delia-Georgeta Dumitras
A re-investigation of ardealite from the type locality, the "dry" Cioclovina Cave (Sureanu Mountains, Romania)
European Journal of Mineralogy (June 2017) 29 (6): 1055-1066

Abstract

Material from the type locality, the "dry" Cioclovina Cave, Sureanu Mountains, Romania, was re-examined in order to update the descriptive mineralogy of ardealite, a rare hydrated calcium acid phosphate sulfate. Ardealite from Cioclovina has a S/P ratio ranging between 1/0.87 and 1/0.98. Although S remains the main tetrahedral cation in the structure, P is consistently present at concentrations between 19.10 and 20.45 wt% P (sub 2) O (sub 5) (0.928-0.992 P atom per formula unit). Concerning the other cations, the mineral shows a very restricted range of composition, without Fe and with very low Mn, Mg, Na and K contents. The indices of refraction are alpha = 1.530(2), beta = 1.537(2) and gamma (calculated for 2V (sub gamma ) = 86 degrees ) = 1.543. The measured density [D (sub m) = 2.335(3)-2.342(5) g/cm (super 3) ] agrees well with the calculated values [D (sub x) = 2.317-2.350 g/cm (super 3) ]. The average unit-cell parameters refined from 31 sets of X-ray powder diffraction data are a = 5.719(5), b = 31.012(28), c = 6.249(7) A and beta = 117.21(6) degrees . Thermally assisted X-ray diffraction analyses confirm that water is lost in three steps; the loss of molecular water is a two-step process and is complete below 250 degrees C. The first thermal breakdown products are brushite and bassanite. The band multiplicity on the IR-absorption spectrum (3nu (sub 3) + 1nu (sub 1) + 3nu (sub 4) + 2nu (sub 2) ) suggests that the protonated phosphate and sulfate groups have C (sub s) point symmetry. The mineral derives from the reaction between calcium carbonate from the moonmilk flows or the cave floor and phosphoric solutions derived from bat guano, with or without hydroxylapatite as a precursor, at pH values up to 5.5.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 29
Serial Issue: 6
Title: A re-investigation of ardealite from the type locality, the "dry" Cioclovina Cave (Sureanu Mountains, Romania)
Affiliation: Romanian Geological Institute, Department of Mineralogy, Bucharest, Romania
Pages: 1055-1066
Published: 20170612
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 41
Accession Number: 2017-082598
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables, geol. sketch map
N45°40'60" - N45°40'60", E23°04'60" - E23°04'60"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201743
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