Enigmatic diamonds from the Tolbachik volcano, Kamchatka

Researchers have discovered approximately 700 diamond crystals within volcanic rocks, primarily pyroclastic, from the Tolbachik volcano in Kamchatka, Russia. These diamonds exhibit cube-octahedral shapes and remarkably homogeneous internal structures. The study employed advanced techniques such as SIMS, scanning and transmission electron microscopy, along with electron energy loss spectroscopy and electron diffraction to analyze these crystals. Two distinct groups of impurity elements were identified: nitrogen (N) and hydrogen (H), which are uniformly distributed, and other elements like chlorine (Cl), fluorine (F), oxygen (O), sulfur (S), silicon (Si), aluminum (Al), calcium (Ca), and potassium (K), which form local concentrations indicating the presence of inclusions. Mineral inclusions within these diamonds, ranging from 70 to 450 nm in size, are primarily Mn-Ni alloys and silicides, with varying stoichiometries and compositions. These inclusions also contain nanometer-sized bubbles with fluid or gas phases, including fluorine and oxygen. Carbon isotopic compositions range from –21 to –29‰ δ13CVPDB, while nitrogen isotopic compositions vary from –2.32 to –2.58‰ δ15NAir. The geological, geochemical, and mineralogical data strongly support the natural origin of these diamonds, formed from volcanic gases during an explosive eruption phase.

Galimov, E. M., Kaminsky, F. V., Shilobreeva, S. N., Sevastyanov, V. S., Voropaev, S. A., Khachatryan, G. K., Wirth, R., Schreiber, A., Saraykin, V. V., Karpov, G. A., & Anikin, L. P. (2020). Enigmatic diamonds from the Tolbachik volcano, Kamchatka. American Mineralogist, 105(4), 498–509. https://doi.org/10.2138/am-2020-7119