Linarite

Abstract: Hoganite, copper(II) acetate monohydrate, and paceite (pronounced ‘paceite’), calcium(II) copper(II) tetraacetate hexahydrate, occur as isolated crystals embedded in ferruginous gossan from the Potosi Pit, Broken Hill, New South Wales, Australia. They are associated with goethite, hematite, quartz, linarite, malachite, azurite, cerussite and cuprian smithsonite. Hoganite is bluish green with a pale blue streak and a Mohs hardness of 13; it possesses perfect {001} and distinct {110} cleavages and has a conchoidal fracture. Chemical analysis of hoganite gave (wt.%) C 23.85; H 3.95; Cu 31.6; Fe 0.4; O (by difference) 40.2, yielding an empirical formula of C4H7.89O5.07Cu1.00Fe0.01. The simplified formula is C4H8O5Cu or Cu(CH3COO)2.H2O, the mineral being identical to the synthetic compound of the same formula. Single-crystal X-ray data for hoganite are: monoclinic, space group C 2/ c , a = 13.162(3), b = 8.555(2), c = 13.850(3) A, β = 117.08(3)°, Z = 8. The density, calculated from single-crystal data, is 1.910 g cm−3. The strongest lines in the X-ray powder pattern are [ d obs ( I obs) ( hkl )] 6.921 (100) (011); 3.532 (28) (202); 6.176 (14) (200); 3.592 (11) (122); 5.382 (10) (211); 2.278 (10) (204); 5.872 (9) (002). Hoganite (orientation presently unknown) is biaxial positive with α = 1.533(2), β = 1.541(3), γ = 1.554(2), 2V(meas.) = 85(5)°, 2V(calc.) = 76.8°, dispersion is r Y > Z . The mineral is named after Graham P. Hogan of Broken Hill, New South Wales, Australia, a miner and well-known collector of Broken Hill minerals. Paceite is dark blue with a pale blue streak and a Mohs hardness of 13; it possesses perfect {100} and {110} cleavages and has an uneven fracture. Chemical analysis of paceite gave (wt.%) C 21.25; H 5.3; Ca 9.0; Cu 14.1; O (by difference) 50.35, yielding an empirical formula of C8H23.77O14.23Ca1.02-Cu1.00. The simplified formula is C8H24O14CaCu or CaCu(CH3COO)4.6H2O, the mineral being identical to the synthetic compound of the same formula. Unit-cell data (refined from X-ray powder diffraction data) for paceite are: tetragonal, space group I 4/ m , a = 11.155(4), c = 16.236(17) A, Z = 4. The density, calculated from refined cell data, is 1.472 g cm−3. The strongest lines in the X-ray powder pattern are [ d obs ( I obs) ( hkl )] 7.896 (100) (110); 3.530 (20) (310); 5.586 (15) (200); 8.132 (8) (002); 9.297 (6) (101); 2.497 (4) (420); 3.042 (3) (321). Paceite is uniaxial positive with ω = 1.439(2) and e = 1.482(3) (white light); pleochroism is bluish with a greenish tint (O), pale bluish with a greyish tint (E), and absorption O ⩾ E. The mineral is named after Frank L. Pace of Broken Hill, New South Wales, Australia, an ex-miner and well-known collector of Broken Hill minerals.

Abstract: Telluroperite, Pb_3Te^(4+)O_4Cl_2, is a new tellurite from Otto Mountain near Baker, California. The new mineral occurs on fracture surfaces and in small vugs in brecciated quartz veins in direct association with acanthite, bromine-rich chlorargyrite, caledonite, cerussite, galena, goethite, and linarite. Various other secondary minerals occur in the veins, including six new tellurates, housleyite, markcooperite, paratimroseite, ottoite, thorneite, and timroseite. Telluroperite is orthorhombic, space group Bmmb, a = 5.5649(6), b = 5.5565(6), c = 12.4750(14) A, V = 386.37(7) A^3, and Z = 2. The new mineral occurs as rounded square tablets and flakes up to 0.25 mm on edge and 0.02 mm thick. The form {001} is prominent and is probably bounded by {100}, {010}, and {110}. It is bluish-green and transparent, with a pale bluish-green streak and adamantine luster. The mineral is non-fluorescent. Mohs hardness is estimated to be between 2 and 3. The mineral is brittle, with a curved fracture and perfect {001} cleavage. The calculated density based on the empirical formula is 7.323 g/cm^3. Telluroperite is biaxial (–), with very small 2V (~10°). The average index of refraction is 2.219 calculated by the Gladstone-Dale relationship. The optical orientation is X = c and the mineral exhibits moderate bluish-green pleochrosim; absorption: X < Y = Z. Electron microprobe analysis provided PbO 72.70, TeO_2 19.26, Cl 9.44, O≡Cl –2.31, total 99.27 wt%. The empirical formula (based on O+Cl = 6) is Pb_(2.79)Te_(1.03)^(4+)O_(3.72)Cl_(2.28). The six strongest powder X-ray diffraction lines are [d_(obs) in A (hkl) I]: 3.750 (111) 58, 2.857 (113) 100, 2.781 (020, 200) 43, 2.075 (024, 204) 31, 1.966 (220) 30, and 1.620 (117, 313, 133) 52. The crystal structure (R_1 = 0.056) is based on the Sillen X_1 structure-type and consists of a three-dimensional structural topology with lead-oxide halide polyhedra linked to tellurium/lead oxide groups. The mineral is named for the relationship to perite and the dominance of Te (with Pb) in the Bi site of perite.

Abstract: The mineral linarite, ${\mathrm{PbCuSO}}_{4}(\mathrm{OH}{)}_{2}$, is a spin-$1/2$ chain with frustrating nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic exchange interactions. Our inelastic neutron scattering experiments performed above the saturation field establish that the ratio between these exchanges is such that linarite is extremely close to the quantum critical point between spin-multipolar phases and the ferromagnetic state. We show that the predicted quantum multipolar phases are fragile and actually suppressed by a tiny orthorhombic exchange anisotropy and weak interchain interactions in favor of a dipolar fan phase. Including this anisotropy in classical simulations of a nearly critical model explains the field-dependent phase sequence of the phase diagram of linarite, its strong dependence of the magnetic field direction, and the measured variations of the wave vector as well as the staggered and the uniform magnetizations in an applied field.

Abstract: Neutron, time-of-flight, Laue diffraction has been carried out on natural single crystals of linarite, PbCu(SO 4 )(OH) 2 , and caledonite, Pb 5 Cu 2 (SO 4 ) 3 CO 3 (OH) 6 , at 293 K. The structural refinements converged to Rw(F) = 0.085 on the basis of 869 observed reflections for linarite and Rw(F) = 0.066 from 1605 observed reflections for caledonite. The locations of all the hydrogen atoms within these structures were extracted from the refinements, enabling calculation of the hydrogen bonding. Linarite is monoclinic, space group P 2 1 / m , with a 9.682(2), b 5.646(1), c 4.683(6) A, and β 102.66(1)°. It comprises chains of edge-sharing Jahn–Teller-elongated CuO 6 square bipyramids running parallel to the [010] direction, bound together by hydrogen bonds. Between these layers are double PbO 8 and SO 4 layers. The two independent hydrogen atoms have been located and are bound as hydroxyl groups to the oxygen atoms at the corners of the CuO 4 square plane. The H(4) atom has conventional hydrogen bonding. The donor–acceptor distance is 2.924(5) A, and the hydrogen bond is nearly linear, with an angle of 176.1(6)°. The O(4)–H(4) hydroxyl bond distance is 0.952(7) A, and the H(4) ... O(2) hydrogen bond has a length of 1.973(9) A. The H(5) hydrogen atom, however, forms a stronger hydrogen bond, with a donor–acceptor distance of 2.706(5) A and an angle of 171.8(6)°. The O(5)–H(5) hydroxyl bond is lengthened to 1.025(8) A, and the H(5) ... O(4) hydrogen bond is a short 1.687(8) A. Caledonite is orthorhombic, space group Pmn 2 1 with a 20.085(3) A, b 7.141(1) and c 6.563(1) A; like linarite, it comprises chains of edge-sharing Jahn–Teller-elongated CuO 6 square bipyramids, although these chains run parallel to the [001] direction. There are three independent Pb sites, in which Pb is coordinated to nine oxygen ligands, with a range of Pb–O distances of 2.352(4) to 3.571(6) A. Caledonite has three independent hydrogen atoms that similar to those in the linarite structure: they are bound as hydroxyl groups to the oxygen atoms at the corners of the square plane of the axially elongate CuO 6 square bipyramids. The hydrogen bonds in caledonite are all significantly bent, with angles between 160 and 170°; otherwise, the H(1) and H(2) atoms have fairly conventional hydrogen bonding. The donor–acceptor distance for O(1) ... O(4) and O(2) ... O(4) are 2.887(7) and 2.776(6) A, respectively; although the O(1)–H(1) hydroxyl bond at 0.95(1) A is shorter than the O(2)–H(2) hydroxyl bond at 0.98(1) A, the H(1) ... O(4) hydrogen bond, 1.97(1) A in length, is slightly longer than the H(2) ... O(4) hydrogen bond at 1.84(1) A . The O(3)–H(3) hydroxyl bond is 0.946(8) A in length, and the H(3) ... O(8) hydrogen bond is slightly shorter than expected at 1.777(9) A. With the O(3) ... O(8) donor–acceptor distance of 2.711(5) A and the 20° deviation from linearity, this hydrogen bond may be strained.