herbertsmithite

Herbertsmithite is a mineral with the chemical formula ZnCu3(OH)6Cl2, often written Cu3Zn(OH)6Cl2 to emphasize copper and zinc components. It is named in honor of the British mineralogist Herbert Smith. The mineral is notable for its copper-rich composition and its occurrence in hydrothermal copper deposits; in nature it is relatively rare and is studied primarily as a reference material for laboratory investigations and for understanding exotic magnetic states.

The crystal structure features copper ions arranged in two-dimensional layers that form a kagome lattice, a pattern of corner-sharing triangles known for geometric frustration. Zinc ions occupy interlayer sites, separating the copper kagome planes. Each copper ion is typically in a Cu2+ state with spin-1/2, and the magnetic interactions between neighboring copper spins are strongly antiferromagnetic. The resulting frustrated lattice suppresses conventional magnetic order even at very low temperatures.

Herbertsmithite has become a leading experimental system for studying quantum spin liquids, a state in which magnetic moments remain disordered due to quantum fluctuations rather than thermal effects. Magnetic measurements show no long-range order down to tens of millikelvin, despite exchange interactions that are large compared with available temperatures. Real samples often exhibit antisite disorder, with some copper and zinc ions exchanging sites, which introduces magnetic impurities and complicates interpretations.

Research on herbertsmithite employs techniques such as neutron scattering, nuclear magnetic resonance, and muon spin relaxation, and continues to inform theories of frustrated magnetism and quantum spin liquids.