The atacamite family of minerals – a testbed for quantum spin liquids

Abstract

Polymorphism of Cu 2 (OH) 3 Cl coupled with partial substitution of Jahn-Teller active Cu 2+ by other divalent metal cations gives rise to the complex mineralogy of the atacamite family of secondary basic copper chlorides. Herbertsmithite, Cu 3 Zn(OH) 6 Cl 2 , in which Zn substitutes for one quarter of the Cu atoms, provides a lattice of corner-sharing triangles of paramagnetic Cu 2+ (spin 1 2 ) cations, rendering the mineral a perfect realization of a kagome antiferromagnet. Geometric frustration of conventional antiferromagnetism is expected to give rise to exotic ground states, with dynamic magnetic structures that might turn out to be physical realizations of quantum spin liquids. In this paper, a synopsis of the key topological, compositional and behavioural features of minerals in the atacamite family is given, with emphasis on the kagome character of the resulting lattice of Cu 2+ cations.

Copper Minerals at Vesuvius Volcano (Southern Italy): A Mineralogical Review

“…In the studied samples, this mineral is coeval with the Cu-vanadates and silicates, azurite and some oxides (hematite, cuprite). The origin of atacamite is commonly related to the supergene oxidation zone of Cu deposits (i.e., porphyry copper, [7]), especially under arid and saline conditions [59,60]. However, it is also related to fumarolic deposition and to weathering of sulfides in subsea black smoker deposits in deep seawater seafloor hydrothermal sites; in these areas, atacamite and paratacamite are the most stable copper salts at the pH and Eh of cold deep seawater, undersaturated in CaCO 3 , and appear to be the ultimate sink for the Cu leached by the hydrothermal systems from the oceanic crust [61].…”

Kagomé networks of octahedrally coordinated metal atoms in minerals: Relating different mineral structures through octahedral tilting

“…The octahedral framework in spinel has the same 3D kagomé net of corner-connected B 4 tetrahedra as in pyrochlore. Another family of minerals with the same topology is the paratacamite group, of which an example is herbertsmithite, Cu 3 Zn(OH) 6 Cl 2 (Malcherek et al , 2018). In herbertsmithite Cu 2+ cations form the kagomé net and Zn 2+ are the capping cations.…”

“…In the atacamite family of minerals, typified by herbertsmithite, Cu 3 Zn(OH) 6 Cl 2 , the Cu 2+ cations occupy the nodes of a three dimensional (3D) kagomé network of edge-shared Cu(OH,Cl) 6 octahedra. This family of minerals has been studied in detail as candidates for quantum spin liquids (Malcherek et al , 2018). Spinel-group and pyrochlore-group minerals also have 3D kagomé networks, with the nodes forming a corner-connected tetrahedral framework, while alunite-supergroup minerals have two-dimensional kagomé networks.…”

Expanding the Averievite Family, (MX)Cu5O2(T5+O4)2 (T5+ = P, V; M = K, Rb, Cs, Cu; X = Cl, Br): Synthesis and Single-Crystal X-ray Diffraction Study

“…Of particular interest are minerals containing transition metal cations such as Cu 2+ that form various cation arrays with interesting magnetic behavior. The kagome lattice consisting of cornersharing Cu 3 triangles forming a 2D net with regular hexagonal rings is probably the most famous example-such an array is geometrically frustrated, and this feature is responsible for the spin liquid behavior first demonstrated for synthetic herbertsmithite and later observed for other synthetic mineral analogues [4][5][6][7][8][9][10][11]. In order to exhibit a spin liquid property, the kagome array should possess an ideal trigonal (or hexagonal) symmetry, Molecules 2021, 26, 1833 2 of 12 which is absent in most minerals with the kagome arrangement of Cu 2+ magnetic ions.…”