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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 m
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 gypsum starts off as tiny crystals
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 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 then 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 April 6, 2012, 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.”
“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,” said Benning.
The
UK-Spanish study was funded by the Marie Curie EU-FP6 Mineral
Nucleation and Growth Kinetics (MIN-GRO) Research and Training Network
(contract MRTNCT-2006-035488), the School of Earth and Environment at
the University of Leeds, and the Ministerio de Economia y
Competitividad: Project Factoría de Cristalización.
The role and implications of bassanite as a stable precursor phase to gypsum precipitation
Research group at University of Leeds
Source: University of Leeds
