^1,2,3Xiaorong Qin et al. (>10)
American Mineralogist 110, 791-807 Link to Article [https://doi.org/10.2138/am-2024-9374]
¹State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry/ Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China
³University of Chinese Academy of Sciences, Beijing 100049, China
Copyright: The Mineralogical Society of America

Al-hematite occurs in a wide range of terrestrial soils, but the impact of hydrologic factors on the formation and preservation of Al-hematite remains uncertain. Experimental studies indicate that the ratio of the intensity (I) of the (110) reflection to the intensity of the (104) reflection [(I(110)/I(104)] increases with increasing Al content in a series of synthetic Al-hematite analyzed by X-ray diffraction (XRD), whereas the ratio of the full-width at half maximum of the (110) reflection to the full-width at half maximum of the (104) reflection [W(110)/W(104)] decreases. Quantitative constraints were applied to determine the various levels of Al-substituted hematite in a basaltic laterite (a 48-m-long drill hole) from Hainan Island in South China. The spatial correlation between the distribution of hematite with varying Al content and the location of the groundwater table in the basaltic laterite indicates that hydrologic conditions play a crucial role in regulating the formation and preservation of Al-hematite. The weathering of basalt in a stable water-saturated environment with a relatively slower flow rate promotes the formation of Al-poor hematite. Conversely, the formation of Al-rich hematite was favored by a relatively high flow rate and alternating wet and dry conditions above the groundwater table. Additionally, capillary water in the surficial soil facilitates the expulsion of Al during the recrystallization of Al-rich hematite, resulting in the formation of Al-poor hematite in the surficial soil. Observations from landed instruments and ground-based telescopes have led to the longstanding suspicion that Al-hematite exists on the surface of Mars. The potential presence of Al-hematite in certain martian outcrops may suggest the existence of transient liquid water with slightly higher flow rates, such as episodic floods, emphasizing the dynamic hydrologic conditions on Mars. Moreover, this study suggests that visible and near-infrared (VNIR) spectroscopy can be employed to identify and characterize Al-rich hematite. This approach could be employed to assess the potential presence of Al-rich hematite on Mars, aiding in the study of the planet’s hydrologic environment.

¹J.Gattacceca et al.(>10)
Meteoritics & Planetary Science (in Press) (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14359]
¹CNRS, Aix Marseille Univ, IRD, INRAE, CEREGE, Aix-en-Provence, France
Published by arrangement with John Wiley & Sons

CI1 chondrites are rare meteorites with high scientific value. In fact, they are the most chemically primitive meteorites and show evidence of intense parent-body aqueous alteration. They also share strong similarities with samples from Ryugu and Bennu asteroids returned by the JAXA Hayabusa2 and NASA’s OSIRIS-REx missions. In this work, we present a detailed study of the Oued Chebeika 002 meteorite, a ~420 g CI1 chondrite found in Morocco in 2024. We describe its petrography, texture, and mineralogy, with a focus on clay mineralogy. We provide the bulk and mineral chemical composition, as well as the bulk oxygen, iron, and chromium isotopic compositions. Spectroscopic properties were studied by means of infrared and Raman spectroscopies. We also measured the density, grain density and magnetic properties. Our results confirm that Oued Chebeika 002 is a CI1 chondrite, with close similarities to the other five know CI1 chondrites, and samples from Ryugu and Bennu asteroids. Several lines of evidence indicate that Oued Chebeika 002 has suffered no significant terrestrial alteration. It is more pristine in that regard than Alais, Orgueil and Ivuna CI1 chondrites, and more similar to samples from asteroids Ryugu and Bennu. Subtle differences exist between Oued Chebeika 002 and other CI1 chondrites that cannot be accounted for by terrestrial alteration of the latter. For instance, olivine and calcite were not observed. It is also noteworthy that the magnetic mineral assemblage of Oued Chebeika 002 is significantly different from that of Alais, Ivuna and Orgueil, but undiscernible from that of Ryugu samples. Chromium and iron isotopic composition of Oued Chebeika 002 confirms that CI1 chondrites, like Ryugu samples, are distinct from meteorites belonging to the non-carbonaceous and carbonaceous isotopic groups and may have originated from the same region where ice giant planets and Oort Cloud comets were formed.