A mysterious blue mineral, first analysed by scientists at London’s Natural History Museum in 1996, is now on public display in the Museum’s Minerals Gallery.
When first brought to the Museum thirty years ago by broadcaster Anna Grayson, experts – led by the late Dr. Gordon Cressey – were unable to identify the mineral and suspected that it was new to science. It was not until much later that experts described it as aerinite, a rare and complex carbonate-bearing silicate. During the sample’s first analysis, it was thought to be a mixture of different minerals and at the time aerinite did not have an entry on the International X-ray Diffraction Database – one of the reasons why the Museum first considered that it may be new to science.
Dr. Paul Schofield, Principal Researcher and a member of the team who went on to study the mineral properties at the Natural History Museum, said: “It’s fantastic to see this ‘blue mineral’ sample back at the Museum, it created such excitement when Anna brought it in during National Science Week. Working with Gordon to measure and understand the unique properties of aerinite took us to many different laboratories around the country. It was such an exciting time, a journey of scientific discovery.”
Aerinite (meaning ‘blue sky’ in Greek after its intense blue appearance) was first named in 1876, however the complex nature of the mineral meant that its structure was not officially determined until 2004 by a team of researchers in Spain. Up until this point and owing to technological advances made over time in research equipment, the validity of the mineral’s classification was disputed – famed mineralogist Dana even cited it as a “bad or doubtful species” in 1892.
Anna Grayson bought the mineral in 1980 from a roadside stall along a road south of Fez, Morocco, a country that boasts a rich and diverse mineralogy. The stall’s trader thought the rock to be lapis lazuli. A geologist herself and noticing its electric blue hue, different to that of lapis lazuli, Anna brought the mineral to the Museum in 1995, as it was holding an open day for members of the public to bring in specimens for identification. Given its complex characteristics, Gordon’s team subsequently analysed the specimen for over a year.
Anna Grayson said: “When I first saw the mineral on that roadside stall in Morocco, the first thing I noticed was that specific shade of blue. Secondly, the “faces” are at an angle and look as if they have been polished with a sheet of rough sandpaper. This property is known as slickensides and is formed by movement in faults. In a sense it is like fossil earthquakes, recording a tectonically active high-pressure environment.”
Through using Synchrotron X-ray analysis, a method in which electrons are accelerated at nearly the speed of light to produce very intense X-ray beams, alongside reviewing initial X-Ray Diffraction (XRD) data, the Museum’s scientists were able to establish the mineral as aerinite and explain its strikingly blue appearance. The mineral itself is made up of millions of crystal fibres, each less than 1/10,000 of a millimetre in size. Along these fibres run chains of two different iron atoms, Fe²⁺ and Fe³⁺. Electrons ‘jump’ between these atoms, absorbing light as it hits the mineral. Depending on the direction at which light hits the mineral, it can appear to change colour from colourless to its famed vivid blue hue.
The largest mineral of its type to be analysed by the Museum’s team, the analysis of this specimen subsequently allowed experts to realise that other unnamed mineral specimens in its collection could also be classified as aerinite. It was 13 years after the appearance of the ‘blue mineral’ sample that the unique atomic arrangement of aerinite was finally solved by Jordi Rius and their team in Barcelona, which required developing new customised analytical methodologies.
Dr. Paul Schofield continued: “This work is a testament to how studies of the mineral kingdom drive technological and analytical advancements, which in turn support researchers worldwide to uncover the secrets of our natural world and develop the functional materials that are driving the energy transition. Our investigation into this blue mineral garnered a lot of public attention and proved vital in the work of the Museum’s mineralogy team in classifying other specimens both in our collection and new to science. It’s a privilege to now be able to showcase this incredible mineral and to highlight the work our team is doing in understanding our planet’s mineralogy.”
Anna Grayson continued: “The Natural History Museum has been an important part of my life since I was seven years old and Gordon Cressey was one of the most impressive scientists I have ever met. I am so proud the specimen is to be on permanent display. Mineralogy is a science full of beauty and wonder, the foundation for materials science and our modern world. This mineral has more stories to reveal, I am certain, as do all the other wonders of the planet displayed here.”
The blue aerinite mineral is now on display in the Natural History Museum’s Minerals Gallery. Housing some of the world’s finest and rarest mineral treasures, this is a free gallery for Museum visitors.
