INSUBCONTINENT EXCLUSIVE:
A small blue diamond with inclusions, seen as dark spots.Before the massive Hope Diamond came to rest in a Smithsonian exhibit, before the
gem passed among wealthy owners and thieves and French royals, before it acquired its cursed reputation, before it was mined in India, the
diamond was born at hellish depths beneath Earth's crust
Fittingly, the birth of a blue diamond like the Hope requires a complex geologic sequence, a new study published Wednesday in the journal
Nature suggests.Blue diamonds are the rarest diamonds on Earth
A recent survey of 13.8 million diamonds turned up that only 0.02 percent were blue ones
These gemstones form four times deeper in the earth than their colorless cousins, the new report indicates, at depths of at least 400 miles
That's nearly twice as far underground as the International Space Station is above us."We always knew there was something special about
these diamonds," said geologist Jeffrey Post, curator of the mineral collection at the Smithsonian's National Museum of Natural History, who
was not involved with this report
The study authors make "a very compelling argument" that these diamonds formed at greater than typical depths.The origin of blue diamonds
"We knew essentially absolutely nothing about where they grow," said geologist Evan M
Smith, a lead author of the Nature report and a research scientist at the Gemological Institute of America in New York, a nonprofit that
oversees the world's gemstone grading system.Diamonds, you may recall, are crystals of carbon atoms
Geologists had determined that trace impurities, contamination with the element boron, turn diamonds blue
A boron atom can replace a carbon atom in the crystal structure
It is not a perfect substitute, and a loose electron from boron absorbs red light, giving the diamond a blue hue.But that discovery only
Boron sticks to the surface of Earth
There should not be any boron to speak of within the interior, where diamonds grow.To answer the question of where the boron originated,
Smith and his colleagues reviewed 46 blue diamonds - including one that fetched $25 million in 2016 - that were submitted to the Gemological
(The study authors did not study the Hope Diamond itself, but Post said the gem is representative of natural blue diamonds.) The Gemological
Institute of America has access to "more stones than any of us would have access to in our lifetime," Post said
That river of stones passing through graders' hands holds valuable geologic information.Diamonds grow in rock like plants grow in soil
"When a diamond grows, sometimes it can envelop some of the surrounding material and trap it," Smith said
He offered a cinematic parallel: the amber that trapped a mosquito in "Jurassic Park." The carbon crystals trap other minerals that are
known as inclusions."I was able to study those inclusions to identify the minerals and start to build up a picture of the birthplace of blue
Those inclusions are a physical fragment of the diamond nursery.To gem cutters, inclusions are flaws to be carved out
To geologists, though, these are messages from the deep
"If you had to design the perfect capsule to bring something from below, a diamond would be it," Post said.Within the inclusions, Smith
identified the remnants of calcium silicates and other minerals that only form at extreme high pressure
As the diamonds worked their way back toward the surface, the high-pressure minerals within became unstable and shattered
These ruptured minerals left fragments, like shrapnel, stuck in the diamonds
"It kind of looks like the inclusion has exploded, almost," Smith said.An analysis of these ruptures, plus the list of minerals found in the
inclusions, pointed to an unusual birthplace
It required the union of two rocks: oceanic crust from the surface and the underlying ocean mantle
That is a match made in the abyss - where the motion of tectonic plates forces a slab of ocean crust to descend like a conveyor belt for
hundreds of miles.This descent can also explain the wayward boron, Smith said
He hypothesized that the rocks in descending crust carried the boron below, as if the element were on a gondola ride to the lower mantle
"That is a good circumstantial bit of evidence, at least," Post said.He said this study cannot prove the origin of the boron but that no
better competing theory exists
The most compelling analysis, a direct evaluation of boron in blue diamonds, would be destructive
The Smithsonian has acquired a few blue diamonds, mostly scraps from cut gems, it is willing to sacrifice, Post said
He's just waiting for researchers to propose an experimental design that can justify destroying some of the priciest minerals on
Earth.(Except for the headline, this story has not been edited by TheIndianSubcontinent staff and is published from a syndicated feed.)
