Nav: Home

Biggest and best diamonds formed in deep mantle metallic liquid

December 15, 2016

Washington, DC--New research from a team including Carnegie's Steven Shirey and Jianhua Wang explains how the world's biggest and most-valuable diamonds formed--from metallic liquid deep inside Earth's mantle. The findings are published in Science.

The research team, led by Evan Smith of the Gemological Institute of America, studied large gem diamonds like the world-famous Cullinan or Lesotho Promise by examining their so-called "offcuts," which are the pieces left over after the gem's facets are cut for maximum sparkle. They determined that these diamonds sometimes have tiny metallic grains trapped inside them that are made up of a mixture of metallic iron and nickel, along with carbon, sulfur, methane, and hydrogen.

These inclusions indicate that the diamonds formed, like all diamonds, in the Earth's mantle, but they did so under conditions in which they were saturated by liquid metal. As unlikely as it sounds, their research shows that pure carbon crystalized from this pool of liquid metal in order to form the large gem diamonds.

"The existence of this metal mixture has broad implications for our understanding of deep Earth processes," Smith said.

Diamonds form deep in the Earth's mantle and shoot to the surface in minor volcanic eruptions of magma. Impurities contained inside diamonds can teach geologists about deep Earth chemistry under the pressure, temperature, and chemical conditions in which they were formed. Diamonds, once formed, have a unique ability to protect and shield any minerals contained inside their crystal structures, thereby giving scientists a special, protected sample of the mantle mineralogy and a glimpse at conditions miles beneath the planet's surface.

Most diamonds form at depths around 90-150 miles under the continents. But so-called "superdeep" diamonds form much deeper--at depths below 240 miles, where the mantle rocks are known to be mobile due to convection. From the team's work, we now understand for the first time that large gem diamonds are a group of superdeep diamonds, according to analysis of tiny samples of silicate that were also found inside the studied diamonds. These tiny silicate inclusions are also associated with the metal.

So what do these tiny samples of metal, along with their associated methane and hydrogen, tell scientists about the deep mantle? It tells them about oxygen availability in different parts of the mantle.

Near the surface, the mantle chemistry is more oxidized, which scientists can tell from the presence of carbon in the form of carbon dioxide in magmas erupted in volcanoes (among other indications). But deeper down, according to the team's findings, some regions of the mantle are the opposite of oxidized, or reduced, which is what allows the iron-nickel liquid metal to form there.

"The fact that reduced regions can be found in the Earth's mantle has been theoretically predicted, but never before confirmed with actual samples" Shirey explained.

"This result provides a direct link between diamond formation and deep mantle conditions, addressing a key goal of the Deep Carbon Observatory," said DCO Executive Director and Carnegie scientist Robert Hazen. "The fact that it was made possible by a hugely successful collaboration between our Diamonds and Mantle Geodynamics of Carbon group and the Gemological Institute of America is also very exciting, highlighting the importance of academic connections with industry and their important role in providing postdoctoral funding and the key specimens for this research."
-end-


Carnegie Institution for Science

Related Carbon Articles:

Carbon storage from the lab
Researchers at the University of Freiburg established the world's largest collection of moss species for the peat industry and science
Carbon-carbon covalent bonds far more flexible than presumed
A Hokkaido University research group has successfully demonstrated that carbon-carbon (C-C) covalent bonds expand and contract flexibly in response to light and heat.
Metal wires of carbon complete toolbox for carbon-based computers
Carbon-based computers have the potential to be a lot faster and much more energy efficient than silicon-based computers, but 2D graphene and carbon nanotubes have proved challenging to turn into the elements needed to construct transistor circuits.
Cascades with carbon dioxide
Carbon dioxide (CO(2)) is not just an undesirable greenhouse gas, it is also an interesting source of raw materials that are valuable and can be recycled sustainably.
Two-dimensional carbon networks
Lithium-ion batteries usually contain graphitic carbons as anode materials. Scientists have investigated the carbonic nanoweb graphdiyne as a novel two-dimensional carbon network for its suitability in battery applications.
Can wood construction transform cities from carbon source to carbon vault?
A new study by researchers and architects at Yale and the Potsdam Institute for Climate Impact Research predicts that a transition to timber-based wood products in the construction of new housing, buildings, and infrastructure would not only offset enormous amounts of carbon emissions related to concrete and steel production -- it could turn the world's cities into a vast carbon sink.
Investigation of oceanic 'black carbon' uncovers mystery in global carbon cycle
An unexpected finding published today in Nature Communications challenges a long-held assumption about the origin of oceanic black coal, and introduces a tantalizing new mystery: If oceanic black carbon is significantly different from the black carbon found in rivers, where did it come from?
First fully rechargeable carbon dioxide battery with carbon neutrality
Researchers at the University of Illinois at Chicago are the first to show that lithium-carbon dioxide batteries can be designed to operate in a fully rechargeable manner, and they have successfully tested a lithium-carbon dioxide battery prototype running up to 500 consecutive cycles of charge/recharge processes.
How and when was carbon distributed in the Earth?
A magma ocean existing during the core formation is thought to have been highly depleted in carbon due to its high-siderophile (iron loving) behavior.
New route to carbon-neutral fuels from carbon dioxide discovered by Stanford-DTU team
A new way to convert carbon dioxide into the building block for sustainable liquid fuels was very efficient in tests and did not have the reaction that destroys the conventional device.
More Carbon News and Carbon Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.