Hellyerite

Abstract: Summary. Nickel carbonate occurs in nature as a hexahydrate (hellyerite) and as a hydroxyhydrate (zaratite), but the anhydrous species is only known as an artificial product. All of the compounds show anomalous properties that have led t.o confusion in the literature. Only the calcite structure was found for NiC0 3 ; hydrothermal conditions appear to be essential for its synthesis, and a variation in cell size was found with changes in duration or temperature of synthesis, or both. Hellyerite probably is [Ni(H 2 0)6] C0 3 , which would explain its ease of decompo­ ~ition and rarity in nature. Zaratite is not a single mineral, but a composite of aInorphous and fibrous components. The conditions under which NiC0 3 might be t'xpected to occur are discussed. Nickel bicarbonate formed in the reactions to produce NiC0 3 ; its X-ray diffraction pattern, indicating cubic symmetry, analysis, and optical properties are given. The behaviour of nickel in these compounds is best explained in terms of crystal held theory.