Scientists discover initial stages by which gypsum crystals form

Apr 05, 2012
This is a photo-composite showing at left giant gypsum crystals up to 11 meters long in the Cave of Crystals, Naica, Chihuahua, Mexico, and at right tiny assembled bassanite nanoscrystals just before they transform to gypsum as produced by the researchers in the lab. Left-hand photo credited to Javier Trueba Right-hand high-resolution microphotograph credited to Liane G. Benning, University of Leeds

Gypsum is a naturally occurring mineral which is often used in industrial processes and which in nature, if left alone for thousands of years, can grow into huge translucent, towering and eerie, crystals more than 10 metres tall. These are famed for their beauty in places such as the Cave of Crystals in Mexico. Nevertheless, the formation of gypsum has until now been largely unexplored.

A study by researchers from the School of Earth and Environment at the University of Leeds and the Laboratorio de Estudios Cristalográficos CSIC-University of Granada found that starts off as tiny of a mineral called bassanite. Most of us know this as Plaster of Paris as we use it in building, art-work, casts and fireproofing. Currently bassanite plaster is manufactured at a rate of 100 million tons per year by dehydrating quarried gypsum at 150 deg C. Builders, artists and medical specialists buy the bassanite powder and add water to create a malleable material that hardens once dried again.

By experimenting with supersaturated gypsum solutions, the researchers were able to produce bassanite at room temperature. This than transforms to gypsum.

Professor Liane G Benning from the University of Leeds said: "This process has never been documented before. In nature gypsum grows as these fantastic large crystals, yet we show that in the lab gypsum actually grows through the assembly of many, tiny bassanite crystals. These link together like a string of pearls before they crystallize to gypsum. We studied hundreds of high-resolution images and caught the tiny bassanite crystals in the act of assembling into gypsum"

Their findings are published today (April 6) in the journal Science.

The lead author, Alexander van Driessche from the Laboratorio de Estudios Cristalográficos in Grenada said: "Our study shows a new, low cost and low temperature way of making bassanite, although so far we have only managed to keep it stable for up to one hour."

This finding may also be applicable for reducing the clogging of pipes and filters through the precipitation of gypsum during water desalination or oil production. It can cost millions of pounds to remove gypsum from a pipe – a serious economic problem specifically for countries supplying much needed drinking water.

Prof. Juan Manuel Garcia Ruiz, the director of the Laboratorio de Estudios Cristalográficos in Granada said: "The study reveals how a natural mineral forming process can have important economic consequences for our daily lives. It also tells us how nature can make such beautiful and enormous crystals as seen in the caves at Naica or even the gypsum and bassanite, recently documented on Mars".

Finally, Prof. Benning said" If we manage to produce and stabilize bassanite crystals at room temperature through a clean, green method for long periods, we don't just learn something about a natural process but, compared to what is industry standard currently, our research could also lead to a massive cost and energy saving for the production of plaster".

Explore further: Study helps uncover mechanism behind solid-solid phase transitions

More information: The role and implications of bassanite as a stable precursor phase to gypsum precipitation by A.E.S. Van Driessche, L.G. Benning, J.D. Rodriguez-Blanco, M. Ossorio, P. Bots and J.M. Garcia-Ruiz is published in Science on April 6, 2012.

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Tennex
not rated yet Apr 05, 2012
It's an application of the well known Ostwald's step rule, in which the thermodynamically metastable modification is usually precipitated first. The probably best known example is the precipitation of white phosphorus from solution or vapors, which is metastable and it transforms spontaneously into more stable darker phosphorus. The stalagmites are crystallizing like the aragonite crystals first, just gradually they're transformed into calcite. You can note the temporal formation of metastable yellow modification of mercury iodide at the video here. In dense aether model even the visible matter around black holes is sorta metastable phase formed temporarily during cosmological phase transitions (an analogy of Wilson cloud). In biology and sociology the fast evolutionary changes are followed with temporal formation of more complex metastable forms too, for example during social revolutions various freaks are gaining attention