¹Masaaki Miyahara,²Takaaki Noguchi,³Akira Yamaguchi,¹Toru Nakahashi,¹Yuto Takaki,^2,4Toru Matsumoto,⁵Naotaka Tomioka,²Akira Miyake,²Yohei Igami,⁶Yusuke Seto
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14370]
¹Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima, Japan
²Division of Earth and Planetary Sciences, Kyoto University, Kyoto, Japan
³National Institute of Polar Research, Tokyo, Japan
⁴The Hakubi Center for Advanced Research, Kyoto University, Kyoto, Japan
⁵Kochi Institute for Core Sample Research, X-star, JAMSTEC, Nankoku, Japan
⁶Department of Geosciences, Osaka Metropolitan University, Osaka, Japan
Published by arrangement with John Wiley & Sons

Djerfisherite, a K-bearing Fe-Ni sulfide, was identified in grain C0105-042 collected from the subsurface of asteroid Ryugu through SEM and TEM analyses. The mineral occurs as an isolated crystal embedded within a matrix of Mg-Fe phyllosilicates. Although djerfisherite is known to form as a condensate phase in enstatite chondrites and aubrites, its mode of occurrence in Ryugu grain C0105-042 is markedly different. Two possible origin scenarios are considered: (i) an extrinsic origin, in which a djerfisherite fragment derived from enstatite chondrites or aubrites was deposited onto asteroid Ryugu, and (ii) an intrinsic origin, where djerfisherite formed in situ through a localized reaction between K-bearing hot fluid or vapor and Fe-Ni sulfide under reducing alkaline conditions within asteroid Ryugu’s body. Isotopic data, which could directly constrain its origin, are currently unavailable; thus, the origin of djerfisherite remains unresolved. Nonetheless, this finding suggests the presence of exotic material or localized chemical heterogeneities within Ryugu’s body, offering new insights into the complex evolutionary processes that shaped primitive bodies in the early Solar System.

¹Naotaka Tomioka,^2,3Kosuke Kurosawa,⁴Akira Miyake,⁴Yohei Igami,⁵Takayoshi Nagaya,⁴Takaaki Noguchi,⁴Toru Matsumoto,⁶Masaaki Miyahara,⁷Yusuke Seto
American Mineralogist 110, 945-955 Link to Article [https://doi.org/10.2138/am-2024-9540]
¹Kochi Institute for Core Sample Research, X-star, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Nankoku, Kochi 783-8502, Japan
²Department of Human Environmental Science, Graduate School of Human Development and Environment, Kobe University, 3-11, Tsurukabuto, Nada-ku, Kobe, Hyogo 657-8501, Japan
³Planetary Exploration Research Center, Chiba Institute of Technology, Narashino, Chiba 275-0016,Japan
⁴Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
⁵Department of Environmental Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan
⁶Earth and Planetary Systems Science Program, Graduate School of Advanced Science and Engineering, Hiroshima University, Higashihiroshima, Hiroshima 739-8526, Japan
⁷Department of Geosciences, Graduate School of Science & School of Science, Osaka Metropolitan University, Sumiyoshi-ku, Osaka 558-8585, Japan
Copyright: The Mineralogical Society of America

Shock recovery experiments were performed using a two-stage light gas gun to clarify the progressive deformation microstructures of calcite at the submicrometer scale concerning pressure. Decaying compression pulses were produced using a projectile that was smaller than the natural marble target. In two experiments, natural marble samples were shocked to 13 and 18 GPa at the epicenters of the targets. Calcite grains shocked in the pressure range of 1.1–18 GPa were examined using polarized light microscopy and (scanning) transmission electron microscopy. The density of free dislocations in the grains shocked at 1.1–2.2 GPa [108–9 (cm−2)] is comparable to that of unshocked Carrara calcite grains. Subparallel bands of entangled dislocations <1 μm are formed at 4.2 GPa, and strongly entangled dislocations spread throughout the focused ion beam (FIB) sections at 7.3–18 GPa. Dislocations selectively nucleate and entangle near the slip planes at pressures above ∼3 GPa, corresponding to the transition from sharp extinction to undulatory extinction, according to the microstructural evolution with shock pressure. Above ∼6 GPa, the dislocations nucleated homogeneously throughout the calcite crystals. The dislocation microstructure in a calcite grain collected from the asteroid Ryugu particle is similar to that of the experimentally shocked calcite at 4.2 GPa. The estimated pressure of 2–3 GPa, determined through fault mechanics analyses and the presence of dense sulfide minerals in the Ryugu particles, is in line with this pressure.