The new mineral species barlowite, ideally Cu4FBr(OH)6, has been found at the Great Australia mine, Cloncurry, Queensland, Australia. It is the Br and F analogue of claringbullite. Barlowite forms thin blue, platy, hexagonal crystals up to 0.5 mm wide in a cuprite-quartz-goethite matrix associated with gerhardtite and brochantite. Crystals are transparent to translucent with a vitreous lustre. The streak is sky blue. The Mohs hardness is 2–2.5. The tenacity is brittle, the fracture is irregular and there is one perfect cleavage on {001}. Density could not be measured; the mineral sinks in the heaviest liquid available, diluted Clerici solution (D &3.8 g/cm3). The density calculated from the empirical formula is 4.21 g/cm3. Crystals are readily soluble in cold dilute HCl. The mineral is optically non-pleochroic and uniaxial (–). The following optical constants measured in white light vary slightly suggesting a small variation in the proportions of F, Cl and Br: ω 1.840(4)–1.845(4) and ε 1.833(4)–1.840(4). The empirical formula, calculated on the basis of 18 oxygen atoms and H2O calculated to achieve 8 anions and charge balance, is Cu4.00F1.11Br0.95Cl0.09(OH)5.85. Barlowite is hexagonal, space group P63/mmc, a = 6.6786(2), c = 9.2744(3) Å , V = 358.251(19) Å3, Z = 2. The five strongest lines in the powder X-ray diffraction pattern are [d(Å )(I)(hkl)]: 5.790(100)(010); 2.889(40)(020); 2.707(55)(112); 2.452(40)(022); 1.668(30)(220).

Plimerite, ideally ZnFe 3+ 4 (PO 4 ) 3 (OH) 5 , is a new mineral from the Block 14 Opencut, Broken Hill, New South Wales. It occurs as pale-green to dark-olive-green, almost black, acicular to prismatic and bladed crystals up to 0.5 mm long and as hemispherical aggregates of radiating acicular crystals up to 3 mm across. Crystals are elongated along [001] and the principal form observed is {100} with minor {010} and {001}. The mineral is associated with hinsdalite-plumbogummite, pyromorphite, libethenite, brochantite, malachite, tsumebite and strengite. Plimerite is translucent with a pale-greyish-green streak and a vitreous lustre. It shows an excellent cleavage parallel to {100} and {010} and distinct cleavage parallel to {001}. It is brittle, has an uneven fracture, a Mohs' hardness of 3.5À4, D(meas.) = 3.67(5) g/cm 3 and D(calc.) = 3.62 g/cm 3 (for the empirical formula). Optically, it is biaxial negative with a = 1.756(5), b = 1.764(4), g = 1.767(4) and 2V(calc.) of À63º; pleochroism is X pale-greenish-brown, Y pale-brown, Z pale-bluish-green; absorption Z > X > Y; optical orientation XYZ = cab. Plimerite is orthorhombic, space group Bbmm, unit-cell parameters: a = 13.865 (3) Å , b = 16.798(3) Å , c = 5.151(10) Å , V = 1187.0(4) Å 3 (single-crystal data) and Z = 4. Strongest lines in the X-ray powder diffraction pattern are [d (Å ), I, hkl]: . Electron microprobe analysis yielded (wt.%): PbO 0.36, CaO 0.17, ZnO 20.17, MnO 0.02, Fe 2 O 3 29.82, FeO 2.98, Al 2 O 3 4.48, P 2 O 5 32.37, As 2 O 5 0.09, H 2 O (calc) 6.84, total 97.30 (Fe 3+ /Fe 2+ ratio determined by Mössbauer spectroscopy). The empirical formula calculated on the basis of 17 oxygens is Ca 0.02 Pb 0.01 Zn 1.68 Fe 2+ 0.28 Fe 3+ 2.53 Al 0.60 P 3.09 As 0.01 O 17.00 H 5.15. The crystal structure was solved by direct methods and refined to an R1 index of 6.41% for 1332 observed reflections from single-crystal X-ray diffraction data (Mo-Ka radiation, CCD area detector). The structure of plimerite is isotypic with that of rockbridgeite and is based on face-sharing trimers of (Mf 6 ) octahedra which link by sharing edges to form chains, that extend in the b-direction. Chains link to clusters comprising pairs of corner-sharing (Mf 6 ) octahedra that link to PO 4 tetrahedra forming sheets parallel to (001). The sheets link via octahedra and tetrahedra corners into a heteropolyhedral framework structure. The mineral name honours Professor Ian Plimer for his contributions to the study of the geology of ore deposits. *

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Middlebackite is a new supergene mineral formed in the upper levels of the Iron Monarch quarry, South Australia. It occurs as aggregates of blue, prismatic crystals up to 0.3 mm across comprising individual crystals up to 0.05 mm in length associated with atacamite and mottramite. Crystals are translucent with a vitreous lustre and have a pale blue streak. Middlebackite is brittle with one perfect cleavage and uneven fracture. Mohs hardness is ~2. The calculated density is 3.64 g cm–3. Crystals are biaxial (+) with α = 1.663(4), β = 1.748(4) and γ = 1.861(4) (measured in white light). The calculated 2V is 86.7°. Pleochroism is X = colourless, Y = very pale blue and Z = dark sky blue; Z > Y > X. The empirical formula unit, based on six oxygen atoms per formula unit is Cu2.00(C2O4)Cl0.02(OH)1.98. Middlebackite is monoclinic, space group P21/c with a = 7.2597(15), b = 5.7145(11), c = 5.6624(11) Å, β = 104.20(3)°, V = 227.73(8) Å3 and Z = 2. The five strongest lines in the powder X-ray diffraction pattern are [d(Å), (I), (hkl)]: 7.070 (16) (100), 3.739 (100) (11$\bar{1}$), 2.860 (18) (020), 2.481 (12) (12$\bar{1}$) and 2.350 (9) (300). The crystal structure was refined from synchrotron single-crystal X-ray diffraction data to R1 = 0.0341 for 596 observed reflections with F0 > 4σ(F0). The structure is based on sheets of edge- and corner-sharing octahedra parallel to the bc plane. Sheets link in the a direction via oxalate anions.

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Edwardsite, Cu 3 Cd 2 (SO 4 ) 2 (OH) 6 ·4H 2 O, is a new mineral from the Block 14 Opencut, Broken Hill, New South Wales, Australia. It occurs as druses of tabular and bladed crystals up to 0.06 mm in size, associated with niedermayrite and christelite. Edwardsite is pale blue, transparent with vitreous lustre and has excellent cleavage parallel to {100}. Density was not measured but the calculated density, from the empirical formula, is 3.53 g cm À3 and the Mohs hardness is~3. Optically, it is biaxial negative with a~1.74, b = 1.762(4), g~1.77 and 2V calc.~+ 62º. The optical orientation is X = b, Y~a, Z~c. Electron microprobe analysis gave (wt.%): CdO 32.43, CuO 28.06, ZnO 2.26, FeO 0.08, SO 3 20.35, H 2 O calc. (from crystal-structure analysis) 14.14, totalling 99.32. The empirical formula, calculated on the basis of 18 oxygen atoms is Cu 2.77 Cd 1.98 Zn 0.22 Fe 0.01 (SO 4 ) 2.00 (OH) 5.95 ·4.06H 2 O. Edwardsite is monoclinic, space group P2 1 /c, with a = 10.863(2) Å , b = 13.129(3) Å , c = 11.169(2) Å , b = 113.04(3)º, V = 1465.9(5) Å 3 (single-crystal data) and Z = 4. The eight strongest lines in the powder diffraction pattern are [d (Å ), (I/I 0 ), (hkl)]: 9.991. The crystal structure was determined by direct methods and refined to R1 = 3.21% using 1904 observed reflections with F o > 4s(F o ) collected using synchrotron X-ray radiation (l = 0.773418 Å ). The structure is based on infinite sheets of edge-sharing Cuf 6 (f: O 2À , OH) octahedra and Cdf 7 (f: O 2À , H 2 O) polyhedra parallel to (100). The sheets are decorated on both sides by cornersharing (SO 4 ) tetrahedra, which also corner-link to isolated Cdf 6 octahedra, thus connecting adjacent sheets. Moderate-strong to weak hydrogen bonding provides additional linkage between sheets.

Nyholmite, Cd3Zn2(AsO3OH)2(AsO4)2·4H2O, from the Block 14 Opencut, Broken Hill, New South Wales, Australia, is a new Cd-Zn arsenate species, isostructural with the minerals of the hureaulite group. The mineral occurs in a quartz-garnet-arsenopyrite matrix as white globules, tufted aggregates of fibrous crystals and radiating hemispheres of thin, colourless, bladed crystals. Associated minerals are goldquarryite, lavendulan-sampleite, scorodite-strengite and gypsum. Individual crystals are up to 0.2 mm in length and 0.05 mm across. The mineral is transparent to translucent with a vitreous lustre. It is brittle with an uneven fracture and a white streak. The Mohs hardness is 3–3.5 and the calculated density is 4.23 g cm–3 for the empirical formula. Electron microprobe analyses yielded CdO 34.58, ZnO 9.72, MnO 3.59, CuO 3.39, Al2O3 0.20, CaO 0.16, PbO 0.37, As2O5 34.55, P2O5 6.29 totalling 92.85 wt.%. The empirical formula, based on 20 oxygen atoms, is Ca0.03Pb0.02 Cd2.80Al0.04Zn1.24-Cu0.44Mn0.53[(AsO4)3.13(PO4)0.92]Σ4.05H1.91·3.79H2O. Nyholmite is monoclinic, C2/c, a = 18.062(4) Å, b = 9.341(2) Å, c = 9.844(2) Å, β = 96.17(3)°, V = 1651.2(6) Å3 (single-crystal data, at 123 K). The six strongest lines in the X-ray powder diffraction pattern are [d(Å),I,(hkl)]: 8.985,30,(200); 8.283,85,(110); 6.169,25,(111); 4.878,25,(002); 3.234,100,(2, 420); 3.079,65,(222, 511); 2.976’45’(113). The crystal structure was solved by Patterson methods and refined using 2045 observed reflections to R1(F) = 3.73%. The structure is characterized by a kinked, five-membered chain of edge-sharing Mφ6 (φ = unspecified anion) octahedra, or pentamer, that extends in the a direction. The pentamers link by sharing corners to form a sheet in the (001) plane. Pentamers are also linked, via corner-sharing, by (As,P)O4 groups forming thick slabs in the (001) plane. The slabs link in the c direction by cornersharing between octahedra and tetrahedra to form a dense heteropolyhedral framework. Moderate to weak hydrogen-bonding provides additional linkage between the slabs.

We report the results of recent experiments on magnetoplasma modes in circular sheets of 4 He ϩ ions trapped below the surface of superfluid helium at a low temperature. The modes we observe include bulk modes, conventional edge modes, multipole edge modes, and extra satellites of unknown origin. The results are compared with earlier observations of bulk and conventional edge modes. Theories of the modes are reviewed and extended, and a detailed comparison with experiment is carried out.