• DOI:10.1126/science.1215648
• Corpus ID: 9355745

The Role and Implications of Bassanite as a Stable Precursor Phase to Gypsum Precipitation

@article{VanDriessche2012TheRA,
  title={The Role and Implications of Bassanite as a Stable Precursor Phase to Gypsum Precipitation},
  author={Alexander E. S. Van Driessche and Liane G. Benning and Juan Diego Rodr{\'i}guez-Blanco and M. Ossorio and Pieter Bots and Juan Manuel Garc{\'i}a‐Ruiz},
  journal={Science},
  year={2012},
  volume={336},
  pages={69 - 72}
}

• A. V. Van Driessche, L. Benning, +3 authors J. García‐Ruiz
• Published 6 April 2012
• Geology
• Science

Roundabout Gypsum Calcium sulfates are a common but perhaps underappreciated group of minerals used in a number of natural and industrial processes. In many ways, these crystals precipitate from solution in the same way that most other aqueous minerals form; however, mounting evidence suggests that different, unexplored mechanisms may be at work. Van Driessche et al. (p. 69; see the cover) performed high-resolution microscopy of the most common calcium sulfate mineral, gypsum, at various points along time-resolved, fast-quenching growth experiments. The images reveal that gypsum particles actually start out as crystalline nanoparticles of another mineral, bassanite, which then self-assemble into well-ordered nanorods. Finally, the nanorods transform into gypsum following a hydration reaction. The observation that the reaction pathway occurs below the solubility limit of the intermediate phase has wide-ranging implications for biomineralization processes and may provide ways to prevent fouling on the surfaces of desalination membranes. The common mineral gypsum forms when nanoparticles of an undersaturated precursor phase, bassanite, self-assemble into nanorods, followed by ripening. Calcium sulfate minerals such as gypsum play important roles in natural and industrial processes, but their precipitation mechanisms remain largely unexplored. We used time-resolved sample quenching and high-resolution microscopy to demonstrate that gypsum forms via a three-stage process: (i) homogeneous precipitation of nanocrystalline hemihydrate bassanite below its predicted solubility, (ii) self-assembly of bassanite into elongated aggregates co-oriented along their c axis, and (iii) transformation into dihydrate gypsum. These findings indicate that a stable nanocrystalline precursor phase can form below its bulk solubility and that in the CaSO4 system, the self-assembly of nanoparticles plays a crucial role. Understanding why bassanite forms prior to gypsum can lead to more efficient anti-scaling strategies for water desalination and may help to explain the persistence of CaSO4 phases in regions of low water activity on Mars.