Description and unique crystal-structure of waterhouseite, a new hydroxy manganese phosphate species from the Iron Monarch deposit, middleback ranges, South Australia
| dc.contributor.author | Pring, A. | |
| dc.contributor.author | Kolitsch, U. | |
| dc.contributor.author | Birch, W. | |
| dc.date.issued | 2005 | |
| dc.description.abstract | Waterhouseite from the Iron Monarch mine, Iron Knob, South Australia, is a new hydroxy manganese phosphate species that has a unique crystal-structure. The mineral was found in a carbonate-rich zone with gatehouseite, seamanite, rhodochrosite, shigaite, barite, hausmannite and hematite. It occurs as divergent sprays of orange-brown to dark brown bladed crystals up to 1 mm in length but only up to 20 μm in thickness. The crystals are transparent with a pearly luster on cleavages, but it is vitreous to pearly on the tabular faces. The mineral is brittle, with a conchoidal fracture and a yellowish brown streak. There is a perfect cleavage on (100) and a probable cleavage on (001). The crystals show the principal forms {100} (dominant), {010}, {011} and {001}. All crystals are twinned on (100) by non-merohedry. The Mohs hardness is estimated to be ∼4, and the measured density is 3.55(5) g/cm<sup>3</sup> (calculated density is 3.591 g/cm<sup>3</sup>). Crystals are biaxial negative and length-slow, with α 1.730(3), β ∼1.738 and γ 1.738(4), but 2V could not be measured. Interference colors are normal, implying the absence of optical dispersion. The optical orientation is XYZ = bac (pseudo-orthorhombic), and the pleochroism is X pale brownish, Y brown-yellow, Z pale brownish, with absorption Z = X > Y. Electron-microprobe analyses yielded the empirical formula Mn<inf>7.29</inf>[(P<inf>1.81</inf>As<inf>0.07</inf> V<inf>0.04</inf>)<inf>∑1.92</inf>O<inf>7.68</inf>](OH,O) <inf>8.32</inf>, calculated on the basis of 16 O atoms. The simplified formula is Mn<inf>7</inf>(PO<inf>4</inf>)<inf>2</inf>(OH)<inf>8</inf>, in agreement with the crystal-structure determination. The strongest five lines in the powder X-ray-diffraction pattern [d in Å(I)(hkl)] are: 4.436(70)(111), 3.621(100)(202), 3.069 (50)(311), 2.941(40)(013), and 2.780(35)(020). Unit-cell parameters refined from powder-diffraction data, a 11.364(6), b 5.570(2), c 10.455(3) Å, β 96.61(3)°, V 657.4(2) Å <sup>3</sup> (Z = 2), agree very well with those refined from the single-crystal data. The crystal structure was solved by direct methods and refined in space group P2<inf>1</inf>/c to R1(F) = 5.15% and wR2<inf>all</inf>(F<sup>2</sup>) = 16.28% using data from a twinned crystal (by non-merohedry) with 1400 "observed" reflections with F<inf>o</inf>. > 4o-(F<inf>o</inf>). The crystal structure is characterized by a dense, complex framework of Mn(O,OH)<inf>6</inf> octahedra and PO<inf>4</inf> tetrahedra, which are linked by both edges and comers. Two different subunits can be recognized in the structure: arsenoclasite-type strips of edge-sharing octahedra (fragments of brucite-pyrochroite-type sheets of octahedra) and finite chains of edge-sharing octahedra (fragments of infinite rutile-type chains). The PO<inf>4</inf> tetrahedra provide a connection between the strips and the chains. Single-crystal Raman spectra confirm weak hydrogen bonding. A unique feature of the structure is that the single PO<inf>4</inf> tetrahedron shares two of its edges with Mn(O,OH)<inf>6</inf> octahedra. Only two synthetic anhydrous metal arsenates are known that show a corresponding sharing of two edges. The structure of waterhouseite has no equivalent, although the unit-cell parameters reveal some relations with the two chemical analogues allactite, Mn<inf>7</inf>(AsO<inf>4</inf>)<inf>2</inf>(OH)<inf>8</inf>, and raadeite, M9<inf>7</inf>(PO<inf>4</inf>)<inf>2</inf> (OH)<inf>8</inf>. | |
| dc.identifier.citation | Canadian Mineralogist, 2005; 43(4):1401-1410 | |
| dc.identifier.doi | 10.2113/gscanmin.43.4.1401 | |
| dc.identifier.issn | 0008-4476 | |
| dc.identifier.uri | http://hdl.handle.net/2440/16532 | |
| dc.language.iso | en | |
| dc.publisher | Mineralogical Assoc Canada | |
| dc.source.uri | https://doi.org/10.2113/gscanmin.43.4.1401 | |
| dc.title | Description and unique crystal-structure of waterhouseite, a new hydroxy manganese phosphate species from the Iron Monarch deposit, middleback ranges, South Australia | |
| dc.type | Journal article | |
| pubs.publication-status | Published |