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Mineralogical ClassificationAllanpringite: publication of the type-description

21st Dec 2006 10:02 UTCMarco E. Ciriotti Manager

Reference:

â€¢ Kolitsch, U., Bernhardt, H.-J., Lengauer, C.L., BlaÃŸ, G. Tillmanns, E. (2005): Allanpringite, Fe3(PO4)2(OH)3Â·5H2O, a new ferric iron phosphate from Germany, and its close relation to wavellite. European Journal of Mineralogy, 17, 793-801.

Abstract:

Allanpringite is a new ferric iron phosphate with the ideal formula Fe3(PO4)2(OH)3Â·5H2O, and is closely related to wavellite, Al3(PO4)2(OH)3Â·5H2O. Type locality is the dump of the abandoned Grube Mark near Essershausen, ca. 5 km SE of Weilburg/Lahn, Taunus, Hesse, Germany. The mineral occurs as pale brown-yellow, <010> acicular, invariably twinned (by nonmerohedry) crystals which are always intergrown to form bundles of subparallel individuals. The maximum length of crystals is ca. 1.5 mm (usually much smaller); bundles can reach up to about 2 mm. The mineral is associated with beraunite (reddish "oxiberaunite" variety), cacoxenite, strengite and cryptomelane. Allanpringite is translucent to transparent, its streak is white with a pale yellowish tint, and it has a vitreous lustre. It shows a perfect cleavage parallel to the morphological elongation and one good cleavage parallel to {010}. It is brittle and has an uneven fracture, a Mohs hardness of âˆ¼3, and D(meas.) = 2.54(2) g/cm3, D(calc.) = 2.583 g/cm3 (for empirical formula). Optically, it is biaxial positive, with Î± = 1.662(5), Î² = 1.675(5), Î³ = 1.747(5), 2VÎ³(calc.) = 48Â°; pleochroism is strong: X colourless, Y colourless, Z dark yellow; absorption Zâ‰«Xâˆ¼Y; orientation XYZ = **b (pseudoorthorhombic); no visible dispersion. Electron microprobe analysis yielded (wt.%): Fe2O3 47.84, Al2O3 0.34, Mn2O3 0.04; CuO 0.08, P2O5 28.56, F0.02, H2Ocalc 23.49, less Oâ‰¡F 0.01, total 100.36. The empirical formula is (Fe2.98Al0.03)(PO4)2(OH3.02F0.01)Â·4.97H2O, based on 16 O atoms.

Allanpringite is monoclinic, space group P21/n, with a = 9.777(3), b = 7.358(2), c = 17.830(5) Ã…, Î² = 92.19(4)Â°, V = 1281.7(6) Ã…3 (single-crystal data) and Z = 4. Strongest lines in the X-ray powder diffraction pattern are : 8.90(100)(002), 8.41(60)(10-1, 101), 5.870(50)(110), 3.600(50)(021, 02-1), 3.231(80)(204,12-2). The crystal structure has been determined using single-crystal X-ray diffraction data (MoKÎ± radiation, CCD area detector) obtained from a twinned fragment (R(F) = 13.3%). The structure of allanpringite is a monoclinically distorted, pseudo-orthorhombic variant of the orthorhombic structure of its Al-analogue wavellite, Al3(PO4)2(OH,F)3Â·5H2O. Chains of corner-sharing, distorted Fe(O,OH,H2O)6 octahedra parallel to <010> are corner-linked by PO4 tetrahedra. Channels, also parallel to <010>, host a positionally split water molecule. Average Fe-O distances of the three nonequivalent Fe atoms range between 2.014 and 2.021 Ã…. Single-crystal laser-Raman spectroscopy confirms an overall weak hydrogen bonding scheme. The structure of allanpringite is also related to those of kingite and mitryaevaite. The amorphous santabarbaraite has a chemical formula basically identical to that of allanpringite. The name honours Dr. Allan Pring, eminent Australian mineralogist.

21st Dec 2006 11:57 UTCPeter Haas

Added.

21st Dec 2006 12:09 UTCErnst A.J. Burke

The reference should of course be Vol. 18 (2006)!

21st Dec 2006 12:16 UTCPeter Haas

Oh shit, yes. Thank you for pointing this out.

21st Dec 2006 12:21 UTCPeter Haas

Fixed.

28th Dec 2006 19:59 UTCUwe Kolitsch Manager

Forgot to mention that I can send PDF reprints to anyone interested.

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