Samples from Takovo, Serbia (the type locality); Perseverance Mine, Agnew, Australia; and Var, France, were examined by X-ray powder diffraction, infrared and optical absorption spectroscopy, and thermogravimetric and chemical analysis. X-ray powder data are indexed with a hexagonal unit cell, and for the Takovo sample, a : 3.0250, c : 22.595 A; the observed spacings conform with rhombohedral symmetry. The observed cell parameters are closely similar to those of pyroaurite and hydrotalcite. Spectroscopic and chemical data confirm the presence of both molecular water and carbonate ions. The compositions of the Australian and Var samples approximate to Ni6Al2(OH)16(CO3,OH). 4H2O. Similar synthetic materials have been prepared by adding nickel and aluminum chlorides to a CO2-saturated solution of NaOH and heating the product for 10 days or one month at 200–250°C and 1500 bars water-vapor pressure.