Hostname: page-component-cd9895bd7-7cvxr Total loading time: 0 Render date: 2024-12-27T06:01:49.545Z Has data issue: false hasContentIssue false
  • English
  • Français

Fluoro-potassic-pargasite, KCa2(Mg4Al)(Si6Al2)O22F2, from the Tranomaro area, Madagascar: mineral description and crystal chemistry

Published online by Cambridge University Press:  05 July 2018

R. Oberti ,
M. Boiocchi ,
F. C. Hawthorne ,
R. Pagano  and
A. Pagano
R. Oberti*
Affiliation:
CNR-Istituto di Geoscienze e Georisorse, UOS Pavia, via Ferrata 1, I-27100 Pavia, Italy
M. Boiocchi
Affiliation:
Centro Grandi Strumenti, Università di Pavia, via Bassi 21, I-27100 Pavia, Italy
F. C. Hawthorne
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
R. Pagano
Affiliation:
PO Box 37, I20092 Cinisello Balsamo, Milano, Italy
A. Pagano
Affiliation:
PO Box 37, I20092 Cinisello Balsamo, Milano, Italy
*
*E-mail: oberti@crystal.unipv.it
Get access Rights & Permissions [Opens in a new window]

Abstract

Fluoro-potassic-pargasite, ideally AKBCa2C(Mg4Al) (Si6Al2)O22WF2, a new amphibole species, has been found in a skarn in the Tranomaro area, Madgascar. The sample used for the description of the new mineral species is a large single amphibole crystal, 4 mm × 2 mm × 2 cm in size, brownish-black with brownish-yellow phlogopite lamellae adhering to one face of the crystal. Fluoro-potassic-pargasite is brittle, has a Mohs hardness of 6.5 and a splintery fracture; it is non-fluorescent, has perfect {110} cleavage, no observable parting, and has measured and calculated densities of 3.46 and 3.151 g cm−3, respectively. In plane-polarized light, it is pleochroic, X = colourless to very pale grey, Y = very pale grey, Z = colourless; X ^ a = 46.9° (in β obtuse), Y ‖ b, Z ^ c = 31.4° (in β acute). It is biaxial positive, α = 1.638(2), β = 1.641(2), γ = 1.653(2); 2Vobs = 49.6(4)°, 2Vcalc = 53.4°.

Fluoro-potassic-pargasite is monoclinic, space group C2/m, a = 9.9104(2), b = 17.9739(4), c = 5.3205(1) Å, β = 105.534(2)°, V = 913.11(6) Å3, Z = 2. The eight strongest lines in the X-ray powder-diffraction pattern are [d in Å(I)(hkl)]: 3.133(100)(310), 3.270(55)(240), 2.809(47)(330). 8.413(45)(110), 2.698(39)(151), 3.374(31)(131), 2.934(29)(221) and 1.647(29)(461). Electron microp-robe analysis gives SiO2 40.20, Al2O3 17.61, TiO2 0.46, FeO 1.96, Fe2O3 2.51, MgO 16.95, MnO 0.05, CaO 13.18, Na2O 0.99, K2O 3.72, F 2.75, H2Ocalc 0.77, sum 99.99 wt.%. The formula unit, calculated on the basis of 24 (O,OH,F) with (OH + F) = 2 - (2 × Ti), is A(K0.69Na0.28Ca0.04)∑=1.01BCa2.00C(Mg3.64Fe0.242+Mn0.01Al0.79Fe0.273+Ti0.05)∑=5.00T(Si5.80Al2.20)∑=8.00O22W[F1.26(OH)0.74]∑=2.00. The mineral species and name have been approved by the IMA CMNMC (IMA 2009-091).

Keywords

fluoro-potassic-pargasiteamphibolenew mineralelectron-microprobe analysisoptical propertiescrystal-structure refinementMadagascar
Type
Research Article
Information
Mineralogical Magazine , Volume 74 , Issue 6 , December 2010 , pp. 961 - 967
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2010

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Burke, E.A.J. and Leake, B.E. (2004) “Named amphiboles”: a new category of amphiboles recognized by the International Mineralogical Association (IMA), and the proper order of prefixes to be used in amphibole names. The Canadian Mineralogist, 42, 1881–1883.CrossRefGoogle Scholar
Hawthorne, F.C., Oberti, R., Ungaretti, L. and Grice, J.D. (1996) A new hyper-calcic amphibole with Ca at the A site: fluor-cannilloite from Pargas, Finland. American Mineralogist, 81, 995–1002.CrossRefGoogle Scholar
Hawthorne, F.C. and Della Ventura, G. (2007) Short-range order in amphiboles. Pp. 173—221 in: Amphiboles: Crystal Chemistry, Occurrence and Health Issues (F.C. Hawthorne, R. Oberti, G. della Ventura and A. Mottana, editors) Reviews in Mineralogy and Geochemistry, 67, Mineralogical Society of America, Chantilly, Virginia, and the Geochemical Society, St. Louis, Missouri, USA.CrossRefGoogle Scholar
Leake, B.E., Woolley, A.R., Birch, W.D., Burke, E.A.J., Ferraris, G., Grice, J.D., Hawthorne, F.C., Kisch, H.J., Krivovichev, V.G., Schumacher, J.C., Stephenson, N.C.N. and Whittaker, E.J.W. (2003) Nomenclature of amphiboles: additions and revisions to the International Mineralogical Association's amphibole nomenclature. The Canadian Mineralogist, 41, 1355–1370.CrossRefGoogle Scholar
Moine, B., Rakotondrazafy, M., Ramambazafy, A., Rakotondratsima, C. and Cuney, M. (1997) Controls on the urano-thorianite deposits in S-E Madagascar. Proceedings of the UNESCO-IUGSIGCP International Field Workshop on Proterozoic Geology of Madagascar, Antananarivo, Madagascar. 55 pp.Google Scholar
Oberti, R., Sardone, N., Hawthorne, F.C., Raudsepp, M. and Turnock, A.C. (1995) Synthesis and crystalstructure refinement of synthetic fluor-pargasite. The Canadian Mineralogist, 33, 25–31.Google Scholar
Oberti, R., Hawthorne, F.C., Cannillo, E. and Cámara, F. (2007) Long-range order in amphiboles. Pp. 125-172 in: Amphiboles: Crystal Chemistry, Occurrence and Health Issues (F.C. Hawthorne, R. Oberti, G. della Ventura and A. Mottana, editors). Reviews in Mineralogy and Geochemistry, 67, Mineralogical Society of America, Chantilly, Virginia, and the Geochemical Society, St. Louis, Missouri, USA.CrossRefGoogle Scholar
Pouchou, J.L. and Pichoir, F. (1985) ‘PAP’ φ(ρZ) procedure for improved quantitative microanalysis. Microbeam analysis—1985. San Francisco Press, San Francisco, California, USA, pp. 104–160.Google Scholar
Supplementary material: File

Oberti et al. supplementary material

Structure factors

Download Oberti et al. supplementary material(File)
File 135.7 KB
Supplementary material: File

Oberti et al. supplementary material

Cif file

Download Oberti et al. supplementary material(File)
File 30.2 KB