Tag Archives: #diamonds

Deep Diamonds Contain Evidence Of Deep-Earth Recycling Processes (Earth Science)

Diamonds that formed deep in the Earth’s mantle contain evidence of chemical reactions that occurred on the seafloor. Probing these gems can help geoscientists understand how material is exchanged between the planet’s surface and its depths.  

New work published in Science Advances confirms that serpentinite—a rock that forms from peridotite, the main rock type in Earth’s mantle, when water penetrates cracks in the ocean floor—can carry surface water as far as 700 kilometers deep by plate tectonic processes.

“Nearly all tectonic plates that make up the seafloor eventually bend and slide down into the mantle—a process called subduction, which has the potential to recycle surface materials, such as water, into the Earth,” explained Carnegie’s Peng Ni, who co-led the research effort with Evan Smith of the Gemological Institute of America.

An illustration showing how diamonds can offer researchers a glimpse into the processes occurring inside our planet, including deep-Earth recycling of surface material. Artwork by Katherine Cain, courtesy of the Carnegie Institution for Science.

Serpentinite residing inside subducting plates may be one of the most significant, yet poorly known, geochemical pathways by which surface materials are captured and conveyed into the Earth’s depths. The presence of deeply-subducted serpentinites was previously suspected—due to Carnegie and GIA research about the origin of blue diamonds and to the chemical composition of erupted mantle material that makes up mid-ocean ridges, seamounts, and ocean islands. But evidence demonstrating this pathway had not been fully confirmed until now.

The research team—which also included Carnegie’s Steven Shirey, and Anat Shahar, as well as GIA’s Wuyi Wang and Stephen Richardson of the University of Cape Town—found physical evidence to confirm this suspicion by studying a type of large diamonds that originate deep inside the planet.

“Some of the most famous diamonds in the world fall into this special category of relatively large and pure gem diamonds, such as the world-famous Cullinan,” Smith said. “They form between 360 and 750 kilometers down, at least as deep as the transition zone between the upper and lower mantle.”

Sometimes they contain inclusions of tiny minerals trapped during diamond crystallization that provide a glimpse into what is happening at these extreme depths.

This cartoon shows a subducting oceanic plate traveling like a conveyor belt from the surface down to the lower mantle. The white arrows show the comparatively well-established shallow recycling pathway in the top layer of the plate (crust and sediments), that feeds into arc volcanoes. Our new findings from studying diamonds reveal a deeper recycling pathway, shown in light blue. Water infiltrating fractures in the seafloor hydrates the rocks in the interior of the plate (forming “serpentinite”), and these hydrated rocks can sometimes be carried down to the top of the lower mantle. This is a major pathway that transfers water, carbon, and other surficial elements deep down into the mantle.Illustration by Wenjia Fan, W. Design Studio.

“Studying small samples of minerals formed during deep diamond crystallization can teach us so much about the composition and dynamics of the mantle, because diamond protects the minerals from additional changes on their path to the surface,” Shirey explained.

In this instance, the researchers were able to analyze the isotopic composition of iron in the metallic inclusions. Like other elements, iron can have different numbers of neutrons in its nucleus, which gives rise to iron atoms of slightly different mass, or different “isotopes” of iron. Measuring the ratios of “heavy” and “light” iron isotopes gives scientists a sort of fingerprint of the iron.

The diamond inclusions studied by the team had a higher ratio of heavy to light iron isotopes than typically found in most mantle minerals. This indicates that they probably didn’t originate from deep-Earth geochemical processes. Instead, it points to magnetite and other iron-rich minerals formed when oceanic plate peridotite transformed to serpentinite on the seafloor. This hydrated rock was eventually subducted hundreds of kilometers down into the mantle transition zone, where these particular diamonds crystallized.

“Our findings confirm a long-suspected pathway for deep-Earth recycling, allowing us to trace how minerals from the surface are drawn down into the mantle and create variability in its composition,” Shahar concluded.

This work was supported by the Diamonds and Mantle Geodynamics Group of the Deep Carbon Observatory, a U.S. National Science Foundation grant, and the research program of the Gemological Institute of America

Featured image: Examples of rough CLIPPIR diamonds from the Letseng mine, Lesotho. These are the same kinds of diamonds as the ones analyzed in this study. Largest stone is 91.07 carats. Photo by Robert Weldon; copyright GIA; courtesy of Gem Diamonds Ltd.

Reference: Evan M. Smith, Peng Ni, Steven B. Shirey, Stephen H. Richardson, Wuyi Wang and Anat Shahar, “Heavy iron in large gem diamonds traces deep subduction of serpentinized ocean floor”, Science Advances  31 Mar 2021: Vol. 7, no. 14, eabe9773 DOI: 10.1126/sciadv.abe9773

Provided by Carnegie Science

RUDN University Physicists Described a New Type of Amorphous Solid Bodies (Material Science)

Many substances with different chemical and physical properties, from diamonds to graphite, are made up of carbon atoms. Amorphous forms of solid carbon do not have a fixed crystal structure and consist of structural units–nanosized graphene particles. A team of physicists from RUDN University studied the structure of amorphous carbon and suggested classifying it as a separate type of amorphous solid bodies: a molecular amorphic with enforced fragmentation. The results of the study were published in the Fullerenes, Nanotubes and Carbon Nanostructures journal.

Many substances with different chemical and physical properties, from diamonds to graphite, are made up of carbon atoms. Amorphous forms of solid carbon do not have a fixed crystal structure and consist of structural units–nanosized graphene particles. A team of physicists from RUDN University studied the structure of amorphous carbon and suggested classifying it as a separate type of amorphous solid bodies: a molecular amorphic with enforced fragmentation. ©RUDN University

Solid carbon has many allotropic modifications. It means that substances with different chemical and physical properties can be built from one and the same atoms arranged in different structures. The variety of carbon allotropes is due to the special properties of its atoms, namely their unique ability to form single, double, and triple valence bonds. If, due to certain reaction conditions, only single bonds are formed (i.e. the so-called sp³-hybridization takes place), solid carbon has the shape of a three-dimensional grid of tetrahedrons, i.e. a diamond. If the conditions are favorable for the formation of double bonds (sp²-hybridization), solid carbon has the form of graphite–a structure of flat layers made of comb-like hexagonal cells. Individual layers of this solid body are called graphene. These two types of solid carbon structures are observed both in ordered crystals and non-ordered amorphous bodies. Solid carbon is widely spread in nature both as crystalline rock (graphite or diamond) deposits and in the amorphous form (brown and black coal, shungite, anthraxolite, and other minerals).

Unlike its crystalline form, natural amorphous carbon belongs to the sp² type. A major study of the structure and elemental composition of sp² amorphous carbon was conducted at the initiative and with the participation of a team of physicists from RUDN University. In the course of the study, the team also took spectral measurements using photoelectronic spectroscopy, inelastic neutron scattering, infrared absorption, and Raman scattering. Based on the results of the study, the team concluded that sp² amorphous carbon is a fractal structure based on nanosized graphene domains that are surrounded by atoms of other elements (hydrogen, oxygen, nitrogen, sulfur, and so on). With this hypothesis, the team virtually re-wrote the history of amorphous carbon that has been known to humanity since the first-ever man-made fire.

“The discovery and experimental confirmation of the graphene nature of the ‘black gold’ will completely change the theory, modeling, and interpretation of experiments with this class of substances. However, some questions remain unanswered. What does solid-state physics make of this amorphous state of solid carbon? What role does amorphous carbon with sp²-hybridization play in the bigger picture? We tried to find our own answers,” said Elena Sheka, a Ph.D. in Physics and Mathematics, and a Consulting Professor at the Faculty of Physics and Mathematics and Natural Sciences, RUDN University.

The team spent two years thoroughly studying the nature of amorphous carbon. Other results of this ambitious project were published in Fullerenes, Nanotubes and Carbon Nanostructures, Journal of Physical Chemistry C, and Journal of Non-Crystalline Solids, Nanomaterials. Together, these works confirm a breakthrough achieved by the physicists of RUDN University in this complex field of physics.

“We have analyzed many studies on amorphous sp² carbon from the point of view of our general understanding of amorphous solid bodies. Based on our research, we can confirm that it belongs to a new type of amorphous substances,” added Elena Sheka from RUDN University.

References: E. F. Sheka , Ye. A. Golubev & N. A. Popova, “Amorphous state of sp² solid carbon”, Fullerenes, Nanotubes and Carbon Nanostructures, 2020. https://www.tandfonline.com/doi/full/10.1080/1536383X.2020.1815713

Provided by RUDN University

Scientists Make Insta-bling at Room Temperature (Physics)

The breakthrough shows that Superman may have had a similar trick up his sleeve when he crushed coal into diamond, without using his heat ray.

An international team of scientists has defied nature to make diamonds in minutes in a laboratory at room temperature – a process that normally requires billions of years, huge amounts of pressure and super-hot temperatures.

ANU PhD scholar Xingshuo Huang holds the diamond anvil that the team used to make the diamonds in the lab. Credit: Jamie Kidston, ANU

The team, led by The Australian National University (ANU) and RMIT University, made two types of diamonds: the kind found on an engagement ring and another type of diamond called Lonsdaleite, which is found in nature at the site of meteorite impacts such as Canyon Diablo in the US.

One of the lead researchers, ANU Professor Jodie Bradby, said their breakthrough shows that Superman may have had a similar trick up his sleeve when he crushed coal into diamond, without using his heat ray.

“Natural diamonds are usually formed over billions of years, about 150 kilometres deep in the Earth where there are high pressures and temperatures above 1,000 degrees Celsius,” said Professor Bradby from the ANU Research School of Physics.

The team, including former ANU PhD scholar Tom Shiell now at Carnegie Institution for Science, previously created Lonsdaleite in the lab only at high temperatures.

This new unexpected discovery shows both Lonsdaleite and regular diamond can also form at normal room temperatures by just applying high pressures – equivalent to 640 African elephants on the tip of a ballet shoe.

“The twist in the story is how we apply the pressure. As well as very high pressures, we allow the carbon to also experience something called ‘shear’ – which is like a twisting or sliding force. We think this allows the carbon atoms to move into place and form Lonsdaleite and regular diamond,” Professor Bradby said.

Co-lead researcher Professor Dougal McCulloch and his team at RMIT used advanced electron microscopy techniques to capture solid and intact slices from the experimental samples to create snapshots of how the two types of diamonds formed.

“Our pictures showed that the regular diamonds only form in the middle of these Lonsdaleite veins under this new method developed by our cross-institutional team,” Professor McCulloch said.

“Seeing these little ‘rivers’ of Lonsdaleite and regular diamond for the first time was just amazing and really helps us understand how they might form.”

Lonsdaleite, named after the crystallographer Dame Kathleen Lonsdale, the first woman elected as a Fellow to the Royal Society, has a different crystal structure to regular diamond. It is predicted to be 58 per cent harder.

“Lonsdaleite has the potential to be used for cutting through ultra-solid materials on mining sites,” Professor Bradby said.

“Creating more of this rare but super useful diamond is the long-term aim of this work.”

Ms Xingshuo Huang is an ANU PhD scholar working in Professor Bradby’s lab.

“Being able to make two types of diamonds at room temperature was exciting to achieve for the first time in our lab,” Ms Huang said.

The team, which involved University of Sydney and Oak Ridge National Laboratory in the US, have published the research findings in the journal Small.

References : McCulloch, D. G., Wong, S., Shiell, T. B., Haberl, B., Cook, B. A., Huang, X., Boehler, R., McKenzie, D. R., Bradby, J. E., Investigation of Room Temperature Formation of the Ultra‐Hard Nanocarbons Diamond and Lonsdaleite. Small 2020, 2004695. https://doi.org/10.1002/smll.202004695

Provided by Australian National University

Cosmic Diamonds Formed During Gigantic Planetary Collisions (Planetary Science)

It is estimated that over 10 million asteroids are circling the Earth in the asteroid belt. They are relics from the early days of our solar system, when our planets formed out of a large cloud of gas and dust rotating around the sun. When asteroids are cast out of orbit, they sometimes plummet towards Earth as meteoroids. If they are big enough, they do not burn up completely when entering the atmosphere and can be found as meteorites. The geoscientific study of such meteorites makes it possible to draw conclusions not only about the evolution and development of planets in the solar system but also their extinction.

This artist’s concept illustrates a catastrophic collision between two rocky exoplanets in the planetary system BD +20 307, turning both into dusty debris. Image Credit: NASA/SOFIA/Lynette Cook

A special type of meteorites are ureilites. These are fragments of a larger celestial body – probably a minor planet – which was smashed to pieces through violent collisions with other minor planets or large asteroids. Ureilites often contain large quantities of carbon, among others in the form of graphite or nanodiamonds. The diamonds on the scale of over 0.1 and more millimetres now discovered cannot have formed when the meteoroids hit the Earth. Impact events with such vast energies would make the meteoroids evaporate completely. That is why it was so far assumed that these larger diamonds – similar to those in the Earth’s interior – must have been formed by continuous pressure in the interior of planetary precursors the size of Mars or Mercury.

Picture 2: Rock sample from ureilite minor planet
Caption: Photo of a rock sample from the ureilite minor planet, found as a meteorite in the Sahara. Length of the fragments about 2cm. Credits: Oliver Christ

Together with scientists from Italy, the USA, Russia, Saudi Arabia, Switzerland and the Sudan, researchers from Goethe University have now found the largest diamonds ever discovered in ureilites from Morocco and the Sudan and analysed them in detail. Apart from the diamonds of up to several 100 micrometres in size, numerous nests of diamonds on just nanometre scale as well as nanographite were found in the ureilites. Closer analyses showed that what are known as londsdalite layers exist in the nanodiamonds, a modification of diamonds that only occurs through sudden, very high pressure. Moreover, other minerals (silicates) in the ureilite rocks under examination displayed typical signs of shock pressure. In the end, it was the presence of these larger diamonds together with nanodiamonds and nanographite that led to the breakthrough.

Picture 3: Colour coded Raman spectroscopic map of the ureilite studied. diamond (red), graphite (blue). Credits: Cyrena Goodrich

Professor Frank Brenker from the Department of Geosciences at Goethe University explains:

“Our extensive new studies show that these unusual extraterrestrial diamonds formed through the immense shock pressure that occurred when a large asteroid or even minor planet smashed into the surface of the ureilite parent body. It’s by all means possible that it was precisely this enormous impact that ultimately led to the complete destruction of the minor planet. This means – contrary to prior assumptions – that the larger ureilite diamonds are not a sign that protoplanets the size of Mars or Mercury existed in the early period of our solar system, but nonetheless of the immense, destructive forces that prevailed at that time.”

References: Fabrizio Nestola, Cyrena A. Goodrich, Marta Morana, Anna Barbaro, “Impact shock origin of diamonds in ureilite meteorites”, PNAS first published September 28, 2020 doi: https://doi.org/10.1073/pnas.1919067117 link: https://www.pnas.org/content/early/2020/09/22/1919067117

Provided by Goethe University Frankfurt

Carbide Planets May Be Made Of Silica and Diamonds (Astronomy)

Extrasolar planets hosted by stars with sufficiently high carbon-to-oxygen ratios could be made of diamonds and silica, according to new research by Arizona State University and the University of Chicago.

An artist’s impression of a carbide planet with diamond and silica as main minerals. Image ctredit: Shim / ASU / Vecteezy.

When stars and planets are formed, they do so from the same cloud of gas, so their bulk compositions are similar.

A star with a lower carbon to oxygen ratio will have planets like Earth, comprised of silicates and oxides with a very small diamond content.

But exoplanets around stars with a higher carbon to oxygen ratio than our Sun are more likely to be carbon-rich.

Arizona State University researcher Dr. Harrison Allen-Sutter and colleagues hypothesized that these carbide exoplanets could convert to diamond and silicate, if water were present, creating a diamond-rich composition.

To test this hypothesis, the scientists needed to mimic the interior of carbide exoplanets using high heat and high pressure.

To do so, they used high pressure diamond-anvil cells in a lab.

First, they immersed silicon carbide in water and compressed the sample between diamonds to a very high pressure.

Then, to monitor the reaction between silicon carbide and water, they conducted laser heating, taking X-ray measurements while the laser heated the sample at high pressures.

As they predicted, with high heat and pressure, the silicon carbide reacted with water and turned into diamonds and silica.

Therefore, if water can be incorporated into carbide planets during their formation or through later delivery, they could be oxidized and have mineralogy dominated by silicates and diamond in their interiors.

The reaction could produce CH4 at shallower depths and H2 at greater depths that could be degassed from the interior, causing the atmospheres of the converted carbon planets to be rich in reducing gases. Excess water after the reaction can be stored in dense silica polymorphs in the interiors of the converted carbon planets. 

Such conversion of mineralogy to diamond and silicates would decrease the density of carbon-rich planet, making the converted planets distinct from silicate planets in mass–radius relations for the 2–8 Earth mass range.

While Earth is geologically active, the team’s results show that carbide planets are too hard to be geologically active and this lack of geologic activity may make atmospheric composition uninhabitable.

References: Allen-Sutter et al. 2020. Oxidation of the Interiors of Carbide Exoplanets. Planet. Sci. J 1, 39; doi: 10.3847/PSJ/abaa3e