LINK<\/strong><\/a><\/p>\n\n\n\n“Recent findings from sample-return missions targeting carbonaceous asteroids suggest that CI-like (Carbonaceous Ivuna-type) small bodies are more common in the solar system than previously thought. However, the general redox characteristics and variations among CI materials remain largely unexplored due to their limited availability on Earth. Moreover, CI meteorites have likely undergone irreversible terrestrial oxidation, resulting in modifications of the iron speciation and the redox states. In this context, the iron mineralogy of samples from the carbonaceous asteroid Bennu allows us to reassess the redox conditions of CI materials during its formation. We performed X-ray diffraction and M\u00f6ssbauer spectroscopy of two Bennu particles from the hummocky group, as well as Oued Chebeika 002 CI meteorite. We compare their iron speciation to that of other CI and CI-like materials, including samples from the asteroid Ryugu, Orgueil CI meteorite, and Oued Chebeika 002 CI meteorite. The results show that Bennu particles contain substantial amounts of Fe sulfides (pyrrhotite, mackinawite, and pentlandite), along with Fe oxide (magnetite) and Fe-bearing (Mg-rich) phyllosilicates, similar to Ryugu samples. Cryogenic M\u00f6ssbauer analysis indicates no significant contribution from ferric oxyhydroxides (i.e., ferrihydrite) in Bennu and Oued Chebeika 002 samples, confirming the previous electron microscopy observations of those samples. These observations imply that Fe3+ forming ferrihydrite observed in historical CI meteorites (e.g., Orgueil, Alais) results from long-term terrestrial oxidation of Fe2+ in sulfides, especially submicron-sized ones. This further strengthens the view that the actual CI materials and their formation environments are less oxidizing than previously estimated from old CI meteorite falls. The Fe3+\/(Fe3++Fe2+) ratios in phyllosilicates in the hummocky particles range from 50 to 70%, indicating local heterogeneity within individual particles. Whereas similar values have been reported for Bennu samples (determined by X-ray Absorption Near-Edge Structure spectroscopy), Ryugu samples, and Oued Chebeika 002 samples (i.e., \u223c50\u201365% of Fe3+\/(Fe3++Fe2+)phyllosilicates), there may be slightly Fe3+-rich sub-regions (close to\u202f\u223c\u202f70%) in our Bennu particles. Furthermore, we found two distinct mineral assemblages among CI and CI-like materials: (i) relatively well-crystallized phyllosilicates without mackinawite but with pyrrhotite, and (ii) disordered phyllosilicates coexisting with mackinawite, a metastable Fe sulfide. The latter finding is consistent with recent studies of mackinawite in Bennu and Ryugu samples, which suggest its formation at the early stages of CI alteration. Together with previous studies of Bennu, Ryugu, and Orgueil samples, our results suggest that different phyllosilicate assemblages preserve distinct Fe valence states, potentially recording redox conditions associated with different stages of formation. The CI materials have conventionally been regarded as relatively equilibrated and homogeneous, however, our results demonstrate the potential of combining clay mineral crystallinity and Fe valence states to unravel formation histories at a finer scale.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Kana Amano, Jean-Christophe Viennet, Pierre Beck, Sergey Yaroslavtsev, Dimitrios Bessas, Aleksandr Chumakov, Jean-Philippe Celse, Ludovic Delbes, Tomoki Nakamura, Yuma Enokido, Kanako Sakamoto, Shogo Tachibana, Mathieu Roskosz Geochimica et Cosmochimica Acta, Available online 11 September 2026…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[77,9,10,2243,552,1184],"tags":[5719,3872,1771,3273,5007,2777,7307,595,110,6810,330,4590,6974,4899,2414,2693],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/42544"}],"collection":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=42544"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/42544\/revisions"}],"predecessor-version":[{"id":42545,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/42544\/revisions\/42545"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=42544"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=42544"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=42544"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}