Gypsum formation may tell us about water on Mars

A new explanation of how gypsum is formed may change the way we process this important building material, as well as allow us to interpret past water availability on other planets such as Mars, scientists say.
Gypsum is an economically important mineral, extensively used as the commercial construction material Plaster of Paris, with a global production of around 100 billion kilogrammes per year, researchers said.
It is a ubiquitous mineral on the Earth's surface, and is also found on the surface of Mars. Despite its importance, until now researchers have not understood how gypsum grows from ions in solutions.
The formation of gypsum, from concentrated aqueous solutions of calcium sulfate, was thought to be a simple, single-step process.

A multinational team, including researchers from the University of Leeds in the UK, has now shown that gypsum forms through a complex 4-step process - the understanding of this process opens the way to more energy efficient production of plaster.
Researchers examined the process using time resolved synchrotron-based X-ray scattering at Diamond Light Source in the UK and identified and quantified each of the 4 steps of the formation process, highlighting specially that the initial moments in the reaction chain are of particular importance, because they determine the final properties of gypsum.

In this 1st step, tiny sub-3 nanometres elongated particles form the primary building blocks (bricks). In subsequent steps these bricks aggregate, self-assemble and rearrange themselves, and finally transform to gypsum crystals.

"Importantly, we envisage that it is possible to alter this pathway by specifically targeting individual stages. For example we could arrest the reaction at the first stage when only nano-bricks are formed, and thus directly synthesise a highly reactive precursor to Plaster of Paris," said Thomas Stawsky from University of Leeds.
"Since plaster is normally produced by the energy-intensive heating of gypsum, such an approach would drastically reduce the cost of production, and significantly decrease the carbon footprint of the industry," Stawsky said.
"We know that gypsum is naturally found on Mars, so applying our current finding will also help us understand and predict the hydrological conditions at the time of gypsum formation on other planets," said Liane G Benning from University of Leeds.

The findings were published in the journal Nature Communications.