166-15 WHAT DO ATOMIC DEFECTS TELL US ABOUT THE GEOLOGIC HISTORY OF NATURAL GEM DIAMONDS?

Session: Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones

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Diamonds are critical minerals for technological, industrial, and jewelry applications. Despite being desired for their rarity and purity, all diamonds contain imperfections (or defects) in their atomic lattice, some of which generate the properties of diamond that are harnessed for applications. The geology of diamonds is most often explored by study of trapped mineral inclusions that preserve information about the Earth’s mantle where the diamond grew. However, atomic defect structures are created and modified in diamonds from the time they grow in the mantle until unearthed at the surface, sometimes spanning billions of years. These defects preserve information about the geological history of diamonds that is not always evident otherwise. When diamond crystallizes, it incorporates select impurity elements, primarily nitrogen, hydrogen, nickel, silicon, and boron. Nitrogen is by far the most abundant impurity in diamonds and is integrated at growth as single atoms. At elevated temperatures in the mantle over geologic time, nitrogen atoms migrate and aggregate, giving clues to the residence time and temperature since growth. Many diamonds are also plastically deformed in the mantle, creating vacancy defects that migrate and combine with other impurities over time. Subsequently, diamonds are brought to the crust in kimberlitic magmas, erupted, eroded, transported, and buried again, sometimes for billions of years. During residence in the crust, radioactive fluids interact with diamonds in alluvial environments and metamorphic events may heat the diamonds, both of which create changes in the defect structures that are ultimately preserved as a record of the diamonds’ geological history.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9179

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