This week I’m focusing on just one namesake mineral: lonsdaleite. This mineral was named in 1966 after Dame Kathleen Lonsdale, a pioneer in the use of x-rays to study crystals. The name was suggested by Clifford Frondel from Harvard University and when Lonsdale found out about this, she wrote him a letter: “It makes me feel both proud and rather humble that it shall be called lonsdaleite. Certainly the name seems appropriate since the mineral only occurs in very small quantities (perhaps rare would be too flattering) and is generally rather mixed up!”
- Native element mineral
- Found in meteorites and kimberlites
- Type locality: Canyon Diablo meteorite, Meteor Crater, Coconino County, Arizona, USA
- Formula: C
- Crystal system: Hexagonal
- Hardness: 7-8 (hardness varies due to crystal imperfections, theoretical hardness is >10)
- Density: 3.2 g/cm3
Lonsdaleite forms when meteorites containing graphite strike the Earth. The heat and stress associated with the impact transforms graphite to diamond, but since the hexagonal crystal structure of graphite is retained, the product is lonsdaleite – ‘normal’ diamonds have a cubic crystal structure. It was first discovered in the mid 1960s in the Canyon Diablo meteorite. It was found in 200mg of residue from the dissolution of a 5kg meteorite sample. The Canyon Diablo meteorite originated from an asteroid that fell to Earth around 50,000 years ago and formed Meteor Crater in Arizona. So far, around 30,000kg of this meteorite has been collected. Lonsdaleite has been found in other meteorites such as Kenna (from Roosevelt County, New Mexico, USA) and Allan Hills 77283 (from Antarctica) and in soil samples from Tunguska, Russia.
Due to the unique series of circumstances needed for its formation, lonsdaleite is a rare mineral, but it can be synthesised in a laboratory. In 1967, a paper published by Bundy and Kasper described how lonsdaleite can be created by heating well crystallised graphite to temperatures of more than 1000°C under pressures of 15-20GPa.
Lonsdaleite is sometimes referred to as hexagonal diamond and is a polymorph of diamond, graphite and chaoite. This means that these minerals share the same chemical formula (pure carbon) but have different crystal structures. When the crystal structures of diamond and lonsdaleite are compared, the difference between the organisation of the carbon ring layers can be seen. In diamond (cubic), the layers are orientated in the same direction but in lonsdaleite (hexagonal) each layer is a mirror image of the previous one.
In theory, lonsdaleite is harder than diamond. Computer simulations by Zicheng Pan (Shanghai Jiao Tong University, China) show that it can withstand 58% more stress than diamond when a tipped probe is bearing down on it. However, due to lattice defects and impurities, lonsdaleite has a hardness of 7-8.
So who was the woman behind the mineral? Dame Kathleen Lonsdale (née Yardley) was born on 28th January 1903 in Newbridge, County Kildare, Ireland to Harry Yardley and Jessie Cameron. She was the youngest of 10 children. In 1908, her parents split up and her mother moved the family to Seven Kings, Essex, England. Lonsdale studied at the Woodford County High School for Girls but since this school didn’t offer maths and science, she moved to the Ilford County High School for Boys. When she was 16 she enrolled at the University of London’s Bedford College for Women. She initially studied maths but switched to physics and in 1922 she graduated with a BSc at the top of her class.
Professor William Bragg, one of her examiners at the college and a Nobel Prize winner, was impressed by her academic ability and offered her a position on his research team at University College London (UCL) who were working on using x-ray technology to study crystal structures of organic compounds. During her time there, she completed an MSc in physics and her project involved measuring the crystal structure of succinic acid. Lonsdale built her own equipment for this project and published a paper with her collaborator William Thomas Astbury. While completing her masters, Bragg became the director of the Davy-Faraday Research Laboratory at the Royal Institution (RI) so she joined the research team there. She graduated from UCL in 1924.
In 1927, she married fellow student Thomas Lonsdale. They moved to Leeds and had three children between 1929 and 1934. While her husband worked at the British Silk Research Association and completed a PhD on the torsional strengths of metals, she secured a job in the physics department at Leeds University. It was during this time that she discovered that hexamethylbenzene has a flat, hexagonal shape. Even though this discovery went against Bragg’s theory, he still supported her.
After moving back to London in 1934, Lonsdale returned to the RI. While spending time at home looking after her children, she worked on formulae for structure factor tables which led to the publication of ‘Simplified Structure Factor and Electron Density Formulae for the 230 Space-Groups of Mathematical Crystallography’ in 1936. When Bragg died in 1942, Henry Dale became the new director of the Davy-Faraday Research Laboratory but since he was occupied with other duties, Lonsdale led research at the RI.
Lonsdale is famous for being a pioneering woman in STEM for her many achievements; these achievements are even more extraordinary considering the great inequalities in society at the time. In 1945, she became one of the two first female fellows of the Royal Society – the other woman was Marjory Stephenson who was a microbiologist. A year later, Lonsdale moved to UCL and founded the crystallography department. She published a textbook called ‘Crystals and X-Rays’ in 1948 (used copies are still available on amazon.co.uk). She became the first female professor at UCL in 1949 (a professor of chemistry) and a few years later she was an editor in chief for the first three volumes of the International X-Ray Tables. In 1956, she was made Dame Commander of the Order of the British Empire. 10 years later, she became the first female president of the International Union of Crystallography and two years after that she was the first woman to become president of the British Association for the Advancement of Science (now called the British Science Association).
After her husband retired from the Ministry of Transport, they moved to Bexhill-on-Sea. Lonsdale died of cancer on 1st April 1971.
Lonsdale and her husband became Quakers in 1935 and gave shelter to refugees during the war. During World War Two, she refused to register for Civil Defence work so she spent a month in Holloway Jail in 1943; this directed her attention to penal reform. Her desire for world peace was a major part of her life and in 1956, she wrote a book in response to nuclear testing in America, the Soviet Union and Britain called ‘Is Peace Possible?’
UCL’s Kathleen Lonsdale Building is named in her honour. It was built in 1915 for the chemistry department and it is now home to laboratories and offices from other departments including earth sciences, physics and astronomy. The Kathleen Lonsdale Building is currently being redeveloped.
Last year, while auditing the mineral collection at UCL, I came across two anhydrite crystals which were presented to Lonsdale in 1946. This information wasn’t recorded on the collections database so it was a wonderful surprise and it was amazing to handle something which was once in her possession.
I came across two very informative webpages while writing this post. There is BBC 4 Radio interview from 8th November 1967. She discusses her work, her views on women in science and her daily routine which included waking up at three in the morning! Her views were very progressive for the time – it’s easy to forget that this interview was conducted in the 60s when many people were fighting for equal rights. Then there’s a really detailed blog post written by Gregory Gbur called ‘Kathleen Lonsdale: Master of Crystallography‘ which describes her life and work.
Header image from bbc.co.uk
Bundy, F. P., and J. S. Kasper. 1967. Hexagonal Diamond – a New Form of Carbon. The Journal of Chemical Physics, 46(9), 3437-3446
Salzmann C. G., Murray B. J. and Shephard J. J. 2015. Extent of Stacking Disorder in Diamond. Diamond and Related Materials, 59, 69-72