Author: Carolyn Gramling / Source: Science News
Blue diamonds, among the rarest gems on Earth, are born deep inside the planet’s mantle. Yet their blue hue comes from boron, an element far more abundant in Earth’s crust than its mantle.
Using tiny flaws encased within the diamonds, scientists now think they’ve figured out how boron could have ended up at depths where the diamonds form: Subducting ocean plates carried the boron deep into Earth’s interior. The flaws also suggest that blue diamonds are among the deepest to form on Earth.Geologist Evan Smith of the New York City–based Gemological Institute of America and colleagues analyzed mineral inclusions, tiny bits of nondiamond material trapped inside the diamond’s crystal structure, found within 46 blue diamonds. The chemical structure and makeup of these minerals, which were trapped in the diamonds as they formed, point to an origin more than 660 kilometers deep, below the boundary between upper and lower mantle, Smith’s team reports August 1 in Nature. Although all diamonds form within the mantle, most form above that boundary layer (SN 4/30/16, p. 8).
Boron-bearing blue diamonds are extremely rare — and extremely pure, Smith says. “They’re quite often completely flawless.” That made it difficult to gather a large enough sample of inclusion-bearing blue diamonds to be able to say anything about their origins.
First, the researchers studied the inclusions to try to determine how deep the 46 diamonds were born.
The team used Raman spectroscopy, a noninvasive technique that illuminates the diamond inclusions with a laser beam and then measures the wavelengths of light scattered by the inclusions. Those wavelengths…The post Rare blue diamonds are born deep in Earth’s mantle appeared first on FeedBox.