GIA (Gemological Institute of America) Postdoctoral Research Fellow Evan Smith has recently conducted a research that may lead to a breakthrough in the study of origin of diamonds. According to Smith’s research, published in the latest issue of Science magazine, diamonds of exceptional size and quality were formed much deeper in the earth than smaller, more common gem diamonds.
According to Gem Konnect, which reports on the findings of Smith’s research, larger stones were formed within 360-750 km in the convecting mantle, whereas most other gem diamonds form in the lower part of continental tectonic plates at depths of 150–200 km. The research also confirmed a long-standing theory that claims that parts of the deep mantle below about 250 km depth contain small amounts of metallic iron and have limited available oxygen.
In order to advance the understanding of Earth’s deep mantle, hidden beneath tectonic plates and therefore largely inaccessible for scientific observation, the researchers studied the unique properties of diamonds with similar characteristics to large and exceptional stones such as the Cullinan, Constellation and Koh-i-Noor. According to Dr. Wuyi Wang, GIA’s director of research and development and an author of the study, “some of the world’s largest and most valuable diamonds, like the Cullinan or Lesotho Promise, exhibit a distinct set of physical characteristics that have led many to regard them as separate from other, more common diamonds. However, exactly how these diamonds form and what they tell us about the Earth has remained a mystery until now”.
The new research shows these Cullinan-like gems sometimes have small metallic inclusions — or internal characteristics – trapped within them. The metallic inclusions coexist with traces of fluid methane and hydrogen. Some of these exceptional diamonds also contain mineral inclusions “that show the diamonds formed at the extreme depths at 360-750 km in the convecting mantle”, according to the research.