An unknown Ni-Al hydrosilicate

Abstract

An "unknown Ni-Al hydrosilicate" was found in the karstic nickel deposits in the localities Ba and Takovo in Serbia, and Aghios Ioannis in Greece. It occurs in fine-grained bluish-green and green aggregates with takovite and hydrated halloysite. It is an epigenetic product in the karstic nickel deposit. X-ray powder diffraction (XRPD) data are indexed with a monoclinic unit cell, a = 8.524 (4), b = 7.490 (3), c = 24.214 (6) A, b = 104.55 (6)°, V = 1545.9 A3. The thermal study has shown a characteristic dehydroxylation effect at 450 °C, which distinguishes this mineral from takovite and halloysite. The infra-red technique is very sensitive for the detection of the "unknown Ni-Al hydrosilicate": an absorption band between 1250 cm-1 and 1270 cm-1 is very characteristic for this mineral. From chemical analyses of the admixture of this mineral and hydrated halloysite in different proportions from the Aghios Ioannis deposit in Greece, after removal of impurities, the calculated formula is close to Ni2.00 Al2.00...