Black diamonds come from space

Two teams of U.S. researchers have found that carbonados -- or black diamonds -- come from outer space. Helped with funds from the National Science Foundation (NSF), they discovered nitrogen and hydrogen in these porous black diamonds found only in Brazil and the Central African Republic. And these elements are not found in conventional diamonds extracted from mines from volcanic rocks. They think these carbonados were part of asteroids which landed on Earth about 3 billion years ago.

Two teams of U.S. researchers have found that carbonados -- or black diamonds -- come from outer space. Helped with funds from the National Science Foundation (NSF), they discovered nitrogen and hydrogen in these porous black diamonds found only in Brazil and the Central African Republic. And these elements are not found in conventional diamonds extracted from mines from volcanic rocks. They think these carbonados were part of asteroids which landed on Earth about 3 billion years ago.

This research was done by Jozsef Garai and Stephen Haggerty of Florida International University, along with Case Western Reserve University researchers Sandeep Rekhi and Mark Chance. For this project, they used the infrared synchrotron radiation at Brookhaven National Laboratory and a technology named Fourier transform infrared spectroscopy or FTIR (Link to Wikipedia).

So even the NSF agreed that these diamonds come from far beyond the Earth. Here is an explanation.

"Conventional diamonds are mined from explosive volcanic rocks [kimberlites] that transport them from depths in excess of 100 kilometers to the Earth's surface in a very short amount of time," said Sonia Esperanca, program director in the National Science Foundation's Division of Earth Sciences, which funded the research. "This process preserves the unique crystal structure that makes diamonds the hardest natural material known."

Below is a picture of "a typical black and highly porous polycrystalline carbonado-diamond (5.3 cts) from Lencois, State of Bahia, Brazil" (Credit: Jozsef Garai). Here is a link to a larger vesrion and to a smaller one -- but in color. Anyway, even in color, these black porous diamonds don't look that pretty.

A typical black carbonado-diamond

For more information, this research work has been published by the Astrophysical Journal Letters under the title "Infrared Absorption Investigations Confirm the Extraterrestrial Origin of Carbonado Diamonds" (Volume 653, Number 2, Part 2, December 20, 2006). Here is a link to the abstract which further explains how the scientists reached their conclusions.

The FTIR spectra of carbonado diamond mostly depict the presence of single nitrogen impurities and hydrogen. The lack of identifiable nitrogen aggregates in the infrared spectra, the presence of features related to hydrocarbon stretch bonds, and the resemblance of the spectra to CVD and presolar diamonds indicate that carbonado diamonds formed in a hydrogen-rich interstellar environment.
This is consistent with carbonado diamond being sintered and porous, with extremely reduced metals, metal alloys, carbides, and nitrides, light carbon isotopes, surfaces with glassy melt-like patinas, deformation lamellae, and a complete absence of primary, terrestrial mineral inclusions. The 2.6-3.8 billion year old fragmented body was of asteroidal proportions.

Asteroidal proportions? The NSF says that "black diamonds were once the size of asteroids, a kilometer or more in diameter when they first landed on Earth."

Now you can dream about the size of such a diamond or read the full research paper (PDF format, 4 pages, 447 KB), which also available in plain HTML format.

And even if you find such a diamond, please don't ask a jeweler to create a ring for your partner: they're not that pretty!

Sources: National Science Foundation news release, via EurekAlert!, November 9, 2006; and various other websites

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