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August 31, 2012 7:43 pm
Lustrous cubic crystals of fluorite cover a square metre of limestone. In daylight they glow blue, fired by the mineral’s intense fluorescence. In artificial light the colour changes magically to emerald green. The rock, extracted last month from a mine in Weardale, County Durham, is the finest new mineral specimen unearthed in Britain for many years. “It is an amazing find,” says Alan Hart, head of mineralogy at London’s Natural History Museum.
The Weardale Giant, as its discoverers call it, comes from the country’s most specialised mine, which operates only to provide crystals of fluorite (also known as fluorspar) for the mineral collecting trade. Rogerley Mine near Stanhope is the final manifestation of centuries of mining in the North Pennines, exploiting ores laid down through hydrothermal activity in the Permian period, well before the first dinosaurs evolved.
About 260 million years ago, superheated water rich in dissolved minerals rose up through cracks in limestone strata and then spread out through horizontal fissures in the rock. There the minerals crystallised out, as the water cooled very slowly. Besides fluorite, the deposits include attractive crystals of galena, sphalerite, barite, calcite and quartz.
Lead mining, an industry that had dominated Weardale during the 19th century, collapsed in the early 20th century. Extraction of fluorite carried on for longer, to supply steel and chemicals industries, but the last industrial-scale mines closed in the late 1990s.
That left Rogerley, started on a very small scale in the 1970s to extract specimens for collectors by mining into an abandoned limestone quarry. In 1999, it was taken over by a small group of American enthusiasts, who come over to work there for two or three months every summer.
I visited on Rogerley’s last working week of 2012. As a teenage rockhound I had gone through abandoned Pennine mine dumps with hammer and rucksack, smashing open rocks in the hope of finding fine fluorite crystals inside. So I relished the prospect of seeing pristine crystals exactly where they had formed.
My walk along hundreds of metres of Rogerley mine tunnels lived up to my high expectations. Though mud coats many of the surfaces, green crystals often glistened in the light from my miner’s helmet.
“This is old-fashioned, traditional mining on a human scale,” says Jesse Fisher, a Rogerley partner. The tunnels are supported with timbers and extended by drilling and blasting; a vintage railcar, pulled by a battery-powered locomotive, removes the rocks.
Extracting the half-tonne Weardale Giant without damaging its fragile crystals took all the team’s mining expertise. It is now being shipped back to the company’s base in California, and is likely to be a focus of attention at the Tucson Mineral Show, the world’s biggest, in Arizona next February.
The theme of the fair will be “fluorite, colours of the rainbow”. Fluorite occurs in a wider range of colours than any other mineral, depending on the impurities present. Purple is most common in the Pennines, while further south in Derbyshire the mineral has the purple-blue banded appearance known as Blue John.
But the emerald green shown in the Weardale Giant is perhaps the most sought-after of all. When this colour is combined with strong daylight fluorescence the effect is extraordinary. “You really don’t know what colour this fluorite is,” says Ian Jones, a British collector working at Rogerley. “Is it the intense blue you see in daylight? Or the underlying green?”
The Rogerley team offered to sell the Weardale Giant to the Natural History Museum for £100,000. “We had a lot of discussion about acquiring it, because it is magnificent, but we decided that we could not justify it in the present climate,” Hart says.
The museum may get another opportunity. Rogerley mine will reopen for another collecting season next summer and, Hart says, “maybe they will find something even bigger and more magnificent”.
The pursuit of the finer things in light
Scientists at Massachusetts Institute of Technology have made the first films of semiconductor nanocrystals that conduct electricity and are free of cracks, writes Ling Ge.
These tiny crystals, just a few millionths of a millimetre across, could enable the production of better light-emitting diodes (LEDs) for lighting and displays. Other applications include non-invasive medical scanners and detectors for toxins.
It is challenging to control the placement of nanocrystals on a surface, and until now typical films have had fractures that limit their functionality. The MIT researchers have discovered how to control the shape and position of defect-free nanocrystal films, and created patterns on a silicon surface just a thousandth of the diameter of a human hair.
“The trick was to get the film to be uniform and to stick to the silicon dioxide substrate. This was achieved by leaving a thin layer of polymer to coat the surface before depositing the layer of nanocrystals on top of it,” says Tamar Mentzel, an author of the paper published in the journal Nano Letters.
The new technique could make it easier and cheaper to deposit nanocrystals over larger areas and on flexible substrates. Nanocrystals glow with different colours according to their size, and they could be used, for instance, to form the pixels in a new generation of high-resolution screens.
Drugs help worms and germs to thrive
Antibiotics extend the lives of nematode worms by as much as 50 per cent while increasing their activity, research at Durham University shows, writes Pippa Stephens. David Weinkove led the investigation of intestinal microbes in C. elegans worms. His team observed the relationship between levels of folates – nutrients made by E. coli bacteria, the worm’s food source – and its lifespan. Folates, a group of B vitamins, are essential for making and repairing biological molecules such as DNA, but in excess they limit the worms’ lifespan.
An orchid called Acampe rigida, which lives in south-west China, is pollinated by raindrops – the first plant shown to depend on rainfall for its reproduction, according to a study in Annals of Botany
Research published in BMC Biology reported that inhibiting the synthesis of folates through sulphonamide, an antibiotic, extended the worms’ lives by 30 to 50 per cent. The drug was used at low concentrations that did not kill the bacteria.
“People have shown before that killing E. coli makes C. elegans live longer. But the interesting thing about our finding is that we are not killing the bacteria, or even slowing their growth,” says Weinkove. “That is a good outcome if you want to intervene with gut microbes in people.” Killing gut bacteria destroys the natural balance of the human microflora.
The findings could be tested in mice within a year, as a precursor to human trials. The team at Durham also wants to find out whether excessive folates harm the worm directly – or indirectly by changing the bacterial behaviour.
The research will be used as a platform to see if other drugs produce the same result, to avoid the long-term use of antibiotics.
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