Nickelhexahydrite from the Weathered Meteorite Dronino: Variations of Chemical Composition, Crystal Structure, and Genesis

摘要

In 1965, nickelhexahydrite, a natural hexahydrite modification of monoclinic nickel sulfate, was described as a new mineral species with the formula fitting (Ni,Mg,Fe~(2+))SO_4 · 6H_2O in samples from Noril'sk (Krasnoyarsk region, Russia) [1]. This mineral is a typical component of the present-day supergene zone of Ni-rich rocks and, particularly, nickel sulfide ore. Nickelhexahydrite makes up greenish and bluish green finegrained crusts and earthy aggregates (sometimes monomineral, but often associated with other sulfates). This mineral can crystallize from water solutions at a temperature lower than 31.5℃ [2]. It can also be produced by the dehydration of morenosite NiSO_4 · 7H_2O. Nickelhexahydrite is a typical seasonal mineral that is readily dissolved in water and dehydrated in dry air. Such instability and occurrence in close intergrowths with the chemically cognate phases, including the tetragonal dimorph of retgersite, hampers the study of nickelhexahydrite. In particular, the crystal structure was identified only for the synthetic analogue of this mineral.