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European Journal of Mineralogy; April 2008; v. 20; no. 2; p. 271-280; DOI: 10.1127/0935-1221/2008/0020-1789
© 2008 E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
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Articles

Skorpionite, Ca3Zn2(PO4)2CO3(OH)2·H2O, a new mineral from Namibia: description and crystal structure

Werner Krause1,*, Herta Effenberger2, Heinz-Jürgen Bernhardt3 and Olaf Medenbach3

1 Henriette-Lott-Weg 8, 50354 Hürth, Germany
2 Institut für Mineralogie und Kristallographie, Universität Wien, Geozentrum, Althanstraße 14, 1090 Wien, Austria
3 Institut für Mineralogie, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany

* Corresponding author, e-mail: We.Krause{at}t-online.de

Skorpionite, Ca3Zn2(PO4)2CO3(OH)2·H2O, is a new secondary mineral from the Skorpion zinc deposit in south-western Namibia. Associated minerals are tarbuttite, hydrozincite and gypsum. Skorpionite forms colourless needle-like crystals of monoclinic symmetry that are elongated parallel to [001] with dominant {100} and {110}; additional forms are {111}, {221}, {131} and {–101}. D (meas.) = 3.15(3) g/cm3; D (calc.) = 3.17 g/cm3. Skorpionite is optically biaxial negative, {alpha} = 1.5884(10), β = 1.6445 (calc.), {gamma} = 1.6455(10), 2V = 15.0° (5) (589 nm); no dispersion. Optical orientation is Y {wedge} c = 26° (in acute β); Z = b. Means of 17 sets of microprobe analyses gave CaO 30.89, ZnO 28.83, P2O5 25.49, CO2 (calc.) 7.96, H2O (calc.) 6.52, total 99.69 wt.%. The empirical formula (based on 14 oxygen atoms pfu) is Ca3.05Zn1.96(PO4)1.99(CO3)1.00(OH)2.06·0.98H2O. Single-crystal X-ray investigations gave space group C2/c, with unit-cell parameters a = 19.045(3), b = 9.320(2), c = 6.525(1) Å, β = 92.73(2)°, V = 1156.9(4) Å3, Z = 4. ZnO4 and PO4 tetrahedra are corner linked to corrugated sheets. The crystal structure forms a three-dimensional network of [Ca22Zn2(OH)2(PO4)2]0 and [Ca1(CO3)(H2O)]0 layers that are linked by hydrogen bonds and by Ca–O bonds.

Key-words: skorpionite, new mineral, Skorpion mine, Namibia, microprobe analysis, crystal structure, calcium zinc carbonate-phosphate hydroxyhydrate.






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