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Reaction pathways towards the formation of dolomite-analogues at ambient conditions

Carlos Pimentel,C. Pina

Published 2016 in Geochimica et Cosmochimica Acta

ABSTRACT

Abstract In this paper we present results of a study of the crystallisation behaviour of the dolomite-analogues norsethite and PbMg(CO 3 ) 2 at room temperature and atmospheric pressure. Whereas precipitation of norsethite was previously obtained by mixing solutions (Hood et al., 1974; Pimentel and Pina, 2014a,b), we report, for the first time, the synthesis of PbMg(CO 3 ) 2 by using the same method. The formation of both phases was promoted by ageing slurries for periods of time ranging from a few days (norsethite) up to 6 months (PbMg(CO 3 ) 2 ). The crystallisation of both norsethite and PbMg(CO 3 ) 2 occurs by sequences of dissolution–precipitation reactions involving several amorphous and crystalline precursor phases, which were identified and characterised by X-ray diffraction and scanning electron microscopy. Depending on the initial composition and Ba:Mg and Pb:Mg ratios in the slurries, different precursors and reaction kinetics were observed. This demonstrates the existence of different reaction pathways towards the formation of the investigated dolomite-analogues. Our experimental results provide new insights into the possible mechanisms of formation of dolomite and other double carbonates in nature.

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