The crystal structure of kintoreite, PbFe3(PO4)2(OH,H2O)6, has been refined. The mineral is rhombohedral, Rm with a = 7.3310(7), c = 16.885(2) Å, Z = 3; the structure has been refined to R = 3.0% and Rw = 3.0% using 183 observed reflections [I > 2σ(I)]. Kintoreite has the alunite-type structure which consists of sheets of corner-sharing Fe(O,OH)6 octahedra parallel to (001). The sheets are composed of clusters of three corner-linked octahedra which are tilted so that the three apical O atoms form the base of the XO4 tetrahedra. The clusters of octahedra are linked to similar groups by corner-sharing to form six membered rings. The Pb cations occupy the cavities between pairs of octahedral sheets and are surrounded by six oxygen atoms from the tetrahedra and six oxygen atoms from the octahedra to form a very distorted icosahedron. The mean bond lengths for the various coordination polyhedra are X–O 1.55 Å, (X= P, As, S); Fe–(O, OH) 2.01 Å; Pb–O 2.84 Å. The composition of the crystal used in the refinement was PbFe3(PO4)1.3(AsO4)0.4(SO4)0.3(OH,H2O)6. The XO4 anions are disordered, as in beudantite, rather than being ordered, as they are claimed to be in corkite.
The crystal structure of carminite, PbFe2(AsO4)2(OH)2 has been refined. The mineral is orthorhombic, Cccm with a = 16.591(2), b = 7.580(1), c = 12.285(1) Å, Z = 8; the structure has been refined to a conventional R = 3.3% using 913 observed reflections [I>2σ(I)]. The structure contains stepped chains of edge-sharing pairs of Fe(O,OH)6 octahedra; these chains are linked by AsO4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination. The hydrogen bonding network in the structure has been modelled using bond valence calculations.
The crystal structure of mawbyite, PbFee(AsQn)z(OH)2 has been refined. The mineral is monoclinic, CZ/m with a = 9.066(4), b = 6.286(3) c = 7.564(3) A, 13 = 114.857(5) ~ Z = 2; the structure has been refined to a conventional R = 4.3% using 361 observed reflections [I> 3or(I)]. The structure contains chains of edgesharing Fe(O,OH)6 octahedra which are linked by AsO4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination. The hydrogen bonding network in the structure has been modelled using bond valence calculations. Mawbyite is confirmed to be isostructural with tsumcorite and dimorphous with carminite and the relationship between these two structures is discussed.
Duftite, PbCu(AsO 4 )(OH) is orthorhombic, space group P2 1 2 1 2 1 with a = 7.768(1), b = 9. 211(1), c = 5.999(1) A Ê , Z = 4; the structure has been refined to R = 4.6% and Rw = 6.5% using 640 observed reflections [F> 2s(F)]. The structure consists of chains of edge-sharing CuO 6 'octahedra', parallel to c; which are linked via AsO 4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination to form a three dimensional network. The CuO 6 'octahedra' show Jahn-Teller distortion with the elongation running approximately along <627>. The hydrogen bonding network in the structure was characterized using bond valence calculations. 'b-duftite' is an intermediate in the duftite-conichalcite series, which has a modulated structure based on the intergrowth of the two structures in domains of approximately 50 A Ê . The origin of the modulation is thought to be associated with displacements in the oxygen lattice and is related to the orientation of the Jahn-Teller distortion of CuO 6 'octahedra'. Approximately half of the strips show an elongation parallel to <627> while the other strips are elongated parallel to [010]. This ordering results in an increase in the b cell repeat compared to duftite and conichalcite. KEY WORDS: duftite, conichalcite, crystal structure, crystal chemistry, modulated structure. had earlier tentatively proposed the point group 222, on the basis of morphological observations. Guillemin (1956) identified two distinct polymorphs of duftite on specimens from Tsumeb, which he denoted as 'a-dufite' with the unit cell a = 7.81, b = 9.19, c = 6.08 A Ê and 'b-duftite' which has the slightly different unit cell a = 7.49, b = 9.36, c = 5.91 A Ê . He proposed that 'a-dufite' is isomorphous with descloizite, PbZn(VO 4 )(OH), and has the space group Pnam while 'b-duftite' is i s o m o r p h o u s w i t h c o n i c h a l c i t e , CaCu(AsO 4 )(OH), which has the space group P2 1 2 1 2 1 . His chemical analyses suggested that the aform is almost pure PbCu(AsO 4 )(OH) while the b-form has approximately 20% Ca substituted for Pb. While Guillemin (1956) was able to prepare the a-form synthetically his attempts to prepare the b-form were unsuccessful. The
Wycheproofite is a new hydrated sodium aluminium zirconium phosphate from a pegmatite vein in granite at Wycheproof, in northwestern Victoria, Australia. The mineral occurs as compact, finely fibrous masses in small cavities in the quartz/feldspar/muscovite/schorl-bearing pegmatite. The fibrous crystals are between 5 and 10 ~tm wide and up to several mm long. Accompanying minerals include two other zirconium phosphates --kosnarite and a new species, selwynite, the K-analogue of gainesite --as well as wardite, eosphorite, cyrilovite, leucophosphitc, rockbridgeite, a kidwellite-like mineral and saleeite. The wycheproofite aggregates are pale pinkish to brownish orange, with a vitreous to pearly lustre. The streak is colourless, fracture rough, cleavage not observed and the Mohs hardness is between 4 and 5. Optical data are incomplete due to the fibrous nature of the mineral; the indices of refraction are in the range 1.62-1.64. The measured density is 2.83 g cm -3. Chemical analysis gave (wt.%) Na20 6. (100) 040; 4.128 (80) 121; 3.711 (65) 023; 3.465 (60) 030; 8.865 (40) 101; 3.243 (35) 132. The crystal structure has not been solved due to the finely fibrous nature of the material available. The name is for the locality, which in the local Australian Aboriginal language means 'witchie bushes growing on a hilltop'.Data on the third occurrence of kosnarite, KZr2(PO4)3, at Wycheproof are also given.
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