Meurigite is a new hydrated potassium iron phosphate related to kidwellite and with structural similarities to other late-stage fibrous ferric phosphate species. It has been found at four localities so far -the Santa Rita mine, New Mexico, U.S.A.; the Hagendorf-Sud pegmatite in Bavaria, Germany; granite pegmatite veins at Wycheproof, Victoria, Australia; and at the Gold Quarry Mine, Nevada, U.S.A. The Santa Rita mine is the designated type locality. Meurigite occurs as tabular, elongated crystals forming spherical and hemispherical clusters and drusy coatings. The colour ranges from creamy white to pale yellow and yellowish brown. At the type locality, the hemispheres may reach 2 mm across, hut the maximum diameter reached in the other occurrences is usually less than 0.5 ram. A wide variety of secondary phosphate minerals accompanies meurigite at each locality, with dufrenite, cyrilovite, beraunite, rockbridgeite and leucophosphite amongst the most common. Vanadates and uranates occur with meurigite at the Gold Quarry mine.Electron microprobe analysis and separate determination of H20 and CO2 on meurigite from the type locality gave a composition for which several empirical formulae could be calculated. The preferred formula, obtained on the basis of 35 oxygen atoms, is (Ko.ssNao.o3)zo.ss(Fe~l~Alo.16Cuo.o2)z7.~9 (PO4)5.11(CO3)o.2o(OH)6.7.7.25H20, which simplifies to KFe3+(PO4)5(OH)7.8H20. Qualitative analyses only were obtained for meurigite from the other localities, due to the softness and openness of the aggregates. Because of the fibrous nature of meurigite, it was not possible to determine the crystal structure, hence the Mineralogical Magazine, October 1996, Vol. 60, pp. 787- (60)800. The X-ray data were indexed on the basis of a monoclinic unit cell determined from electron diffraction patterns. The cell parameters, refined by least squares methods, are a = 29.52(4), b = 5.249(6), c = 18.26(1) ,~, 13 = 109.27(7) ~ V = 2672(3) ~3, and Z = 4. The calculated density is 2.89 gcm -3. The space group is either C2, Cm or C2/m. X-ray powder data for meurigite are closely similar to those for kidwellite and phosphofibrite, but meurigite appears to be characterised by a strong 14 A reflection. The relationship between these three minerals remains uncertain in the absence of structural data. On the available evidence, meurigite and kidwellite are not the respective K and Na-endmembers of a solid solution series. The meurigite cell parameters suggest it belongs to a structural family of fibrous ferric phosphates, such as rockbridgeite, dufrenite and beraunite, which have a discrete 5 A fibre axis. Meurigite occurs in widely varying environments, its formation probably favoured by late-stage solutions rich in K rather than Na.
Aluminium-bearing strunzite, [Mn 0.65 Fe 0.26 Zn 0.08 Mg 0.01 ] 2+ [Fe 1.50 Al 0.50 ] 3+ (PO 4 ) 2 (OH) 2 ·6H 2 O, occurs as fibrous aggregates in a crystallographically oriented association with jahnsite on altered zwieselite samples from the phosphate pegmatite at Hagendorf Sü d, Bavaria, Germany. Synchrotron X-ray data were collected from a 3 mm diameter fibre and refined in space group P1 to R 1 = 0.054 for 1484 observed reflections. The refinement confirmed the results of chemical analyses which showed that one quarter of the trivalent iron in the strunzite crystals is replaced by aluminium. The paragenesis revealed by scanning electron microscopy, in combination with chemical analyses and a crystal-chemical comparison of the strunzite and jahnsite structures, are consistent with strunzite being formed from jahnsite by selective leaching of (100) metalÀphosphate layers containing large divalent Ca and Mn atoms.
Wilhelmgümbelite, ideally [ZnFe2+Fe33+(PO4)3(OH)4(H2O)5]·2H2O, is a new secondary phosphate mineral related closely to schoonerite, [ZnMnFe22+Fe3+(PO4)3(OH)2(H2O)7]·2H2O, from oxidized zones of the Hagendorf-Süd pegmatite, Hagendorf, Oberpfalz, Bavaria, Germany. Wilhelmgümbelite occurs as radiating sprays of needle-like rectangular laths, up to 0.2 mm long and with colour varying from light yellow brown to orange red. Cleavage is perfect parallel to {010}. The mineral is associated closely with an oxidized pseudomorph of phosphophyllite, recently named steinmetzite. Other associated minerals are albite, apatite, chalcophanite, jahnsite, mitridatite, muscovite and quartz. The calculated density of wilhelmgümbelite is 2.82 g cm–3. It is optically biaxial (+) with α = 1.560(2), β = 1.669(2), γ = 1.718(2), 2V(meas) = 63(1)° and 2V(calc.) = 65°. Dispersion is weak with r > v, orientation X = b, Y = c, Z = a. Pleochroism is weak, with coloursZ = orange brown, Y = yellow brown, X = light yellow brown, Z >> Y > X. Electron microprobe analyses (average of seven analyses, seven crystals) with H2O and FeO/Fe2O3 calculated on structural grounds, gave FeO 5.8, Fe2O3 25.0, MnO 2.6, ZnO 16.4, P2O5 28.7, H2O 23.4, total 101.9 wt.%. The empirical formula, scaled to 3 P and OH– adjusted for charge balance is Zn1.50Mn0.272+Fe0.602+Fe2.333+(PO4)3·(OH)2.73(H2O)8.27. The structural formula is [Zn(Mn0.27Fe0.733+)∑1.0(Zn0.25Fe0.152+Fe0.603+)∑1.0(Zn0.25Fe0.452+)∑0.7Fe3+(PO4)3(OH,H2O)9]·2H2O.Wilhelmgümbelite has orthorhombic symmetry, Pmab, Z = 4, with the unit-cell parameters of a = 10.987(7) Å, b = 25.378(13) Å, c = 6.387(6) Å and V = 1781(2) Å3. The strongest lines in the powder X-ray diffraction pattern are [dobs in Å(Iobs) (hkl)] 12.65 (100) (020); 8.339 (5) (120); 6.421 (14) (001); 6.228 (8) (011); 4.223 (30) (120) and 2.111 (7) (0 12 0). Wilhelmgümbelite is an oxidized form of schoonerite, with the Mn2+ replaced principally by Fe3+. Its structure differs from that of schoonerite in having the Zn partitioned between two different sites, one five-coordinated as in schoonerite and the other tetrahedrally coordinated. Wilhelmgümbelite also differs structurally from schoonerite in having partial occupation of one of the Fe sites, which appears to be correlated with the Zn partitioning.
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