Description and crystal structure of a new mineral, edwardsite, Cu₃Cd₂(SO₄)₂(OH)₆·4H₂O, from Broken Hill, New South Wales, Australia

Abstract

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.

Magnetic Properties of the Spin-1/2 Deformed Kagome Antiferromagnet Edwardsite

“…All diffraction peaks observed in the powder XRD pattern shown in Fig. 1 which are close to those reported for a natural mineral by Elliott et al [14]. The peak width is slightly less than that of a high-quality sample of vesignieite [7], indicating a relatively good crystallinity of the sample.…”

“…Edwardsite, Cd 2 Cu 3 (SO 4 ) 2 (OH) 6 ·4H 2 O, is a natural mineral recently identified by Elliott et al [14]. It crystallizes in a monoclinic structure with the space group of P 2 1 /c; the lattice constants are a = 10.863(2)Å, b = 13.129(3)Å, c = 11.169(2)Å, and β = 113.04(3)…”

Quantum magnetism in minerals

“…This can explain why the thermal Hall effect in volborthite was observed only in high magnetic fields [410]. The author suggests that similar effects can be expected in volborthite and another distorted kagome mineral edwardsite, Cd 2 Cu 3 (SO 4 ) 2 (OH) 6 · 4H 2 O (space group P 2 1 /c) [425], which orders with a canted AFM structure below 4.3 K and has the same orbital arrangement as herbertsmithite [426]. However, high-field magnetization measurements on edwardsite showed a saturated value of only 1/3 of the full expected moment…”

Hodgesmithite, (Cu,Zn)6Zn(SO4)2(OH)10·3H2O, a new copper zinc sulfate mineral with a unique, decorated, interrupted-sheet structure

“…Hawthorne & Schindler (2000) listed 20 mineral structures that are based on decorated [M' 2 ] N sheets. Five additional related minerals have since been discovered: montetrisaite (Orlandi & Bonaccorsi, 2009), edwardsite (Elliott et al, 2010), kobyashevite (Pekov et al, 2013), aldridgeite (Elliott & Pring, 2015) and the subject of this paper, hodgesmithite.…”