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Nature Research, Nature Communications, 1(7), 2016

DOI: 10.1038/ncomms11177

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Formation of calcium sulfate through the aggregation of sub-3 nanometre primary species

Journal article published in 2016 by Tomasz M. Stawski, Alexander E. S. van Driessche, Mercedes Ossorio, Juan Diego Rodriguez-Blanco, Juan Diego Rodriguez-Blanco ORCID, Rogier Besselink ORCID, Liane G. Benning ORCID
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

AbstractThe formation pathways of gypsum remain uncertain. Here, using truly in situ and fast time-resolved small-angle X-ray scattering, we quantify the four-stage solution-based nucleation and growth of gypsum (CaSO4·2H2O), an important mineral phase on Earth and Mars. The reaction starts through the fast formation of well-defined, primary species of <3 nm in length (stage I), followed in stage II by their arrangement into domains. The variations in volume fractions and electron densities suggest that these fast forming primary species contain Ca–SO4-cores that self-assemble in stage III into large aggregates. Within the aggregates these well-defined primary species start to grow (stage IV), and fully crystalize into gypsum through a structural rearrangement. Our results allow for a quantitative understanding of how natural calcium sulfate deposits may form on Earth and how a terrestrially unstable phase-like bassanite can persist at low-water activities currently dominating the surface of Mars.