Whiskers on Tanzanian crystals proclaimed Mineral of the Year

3 July 2017

merelaniite whiskers on calcite

A merelaniite whisker showing naturally unravelling ribbons, some partially enclosed in the mineral calcite © John Jaszczak

Tiny metallic 'whiskers', first spotted by a 14-year-old girl and her father, have been named Mineral of the Year for 2016.

They were determined to be a previously undiscovered mineral species by an international team of scientists.

The new mineral, named merelaniite after the region in Tanzania where it comes from, was awarded the accolade by the International Mineralogy Association.

An exciting discovery

Merelaniite was spotted in 2011 by mineral enthusiast Jessica Simonoff and her father, Bob. Jessica saw the small, silvery-black strands on a crystal of another mineral she was studying.

The same material was coincidentally being studied by a team of scientists who had come across the whiskers in their own research on mineral samples from the same area. They set to work to determine the exact chemical composition and physical structure of the mineral, to see if it was new to science.

As part of that team, Mike Rumsey, the Museum's Senior Curator in Charge of Minerals had a hunch that it would prove interesting. He worked closely with lead author John Jaszczak on the discovery.

'When you curate of one of the world's finest and largest mineral collections, full of exotic specimens formed from nature's grand chemistry set, you get to see a lot of unusual things,' he says.

'These little "whiskers" in the rocks, along with all the beautiful associated minerals, told us we were potentially on to something exciting.'

A scanning electron microscope image of a merelaniite whisker

A scanning electron microscope image of a merelaniite whisker, showing its structure is made of wound-up thin layers © John Jaszczak
 

Atomic patterns

There are over 5,000 known minerals, and around 100 more are discovered every year. Each mineral is made of a different mix of chemical elements, arranged at the atomic level in a particular pattern. This combination gives the mineral its distinctive physical and chemical properties.

The International Mineralogy Association gives its Mineral of the Year award to recognise the most interesting mineral discovery published in the previous year. This can be for 'possessing unique chemical compositions, interesting and complex structures, beautiful crystals, or forming under unusual conditions'.

A scanning electron microscope image of a broken merelaniite whisker

A scanning electron microscope image of a broken merelaniite whisker, revealing the coiled nature of its layered structure © John Jaszczak
 

Unpicking the structure of merelaniite

To the naked eye, merelaniite appears as cylindrical wires. Observing it under an electron microscope reveals thin sheets that wrap up like scrolls of paper.

Museum scientist John Spratt used an electron microprobe to determine what chemical elements were present and in what proportions. Dr Chris Stanley, a researcher at the Museum, determined some of the optical properties of the mineral.

Work by Prof Luca Bindi at the University of Florence then helped the team to determine the mineral's crystal structure - the three-dimensional arrangement of the atoms of the different chemical elements already determined.

The results revealed a complex structure of layers of molybdenum disulphide alternating at the atomic scale with layers of lead sulphide, along with other elements, including vanadium, antimony, bismuth and selenium.

This unusual double-layer structure causes the mineral to curl as it grows, rolling up into its distinctive scroll-like sheets.

Merelaniite whiskers growing through crystals of stilbite

Merelaniite whiskers growing through colourless crystals of stilbite © John Jaszczak
 

Use and ornament

Prof John Jaszczak from Michigan Technological University, who instigated the work, explains that although merelaniite may be less showy than other minerals, it still has its own glamour:

'Minerals also have an internal beauty in their crystal structures and in the way that influences their properties,' he says.

'Learning about minerals with unique crystal structures grants insight into the nature of matter and sometimes leads to new human-made materials - their inspiration comes from natural sources.'

  • By James McNish

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