Replacement of magnetite by hematite in hydrothermal systems: A refined redox-independent model

Remagnetization Under Hydrothermal Alteration of South Tibetan Paleocene Lavas: Maghemitization, Hematization, and Grain Size Reduction of (Titano)magnetite

“…The transformation of magnetite to hematite can occur through solid‐state oxidation by molecular O 2 following Equation (1) (Davis et al., 1968; Dunlop & Ödemir, 1997). It can also proceed via non‐redox interface‐coupled dissolution‐reprecipitation reaction in hydrothermal systems following Equations (2) and (3) (e.g., Ohmoto, 2003; Otake et al., 2007; Yin et al., 2022; Zhao et al., 2019). $$$4{\mathrm{F}\mathrm{e}}_{3}{\mathrm{O}}_{4}(\mathrm{m}\mathrm{a}\mathrm{g}\mathrm{n}\mathrm{e}\mathrm{t}\mathrm{i}\mathrm{t}\mathrm{e})+{\mathrm{O}}_{2}=6{\mathrm{F}\mathrm{e}}_{2}{\mathrm{O}}_{3}(\mathrm{h}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{t}\mathrm{e})$$$ $$${\mathrm{F}\mathrm{e}}_{3}{\mathrm{O}}_{4}(\mathrm{m}\mathrm{a}\mathrm{g}\mathrm{n}\mathrm{e}\mathrm{t}\mathrm{i}\mathrm{t}\mathrm{e})+2{\mathrm{H}}^{+}={\mathrm{F}\mathrm{e}}_{2}{\mathrm{O}}_{3}(\mathrm{h}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{t}\mathrm{e})+{\mathrm{F}\mathrm{e}}^{2...$$…”

“…dissolution-reprecipitation reaction in hydrothermal systems following Equations ( 2) and ( 3) (e.g., Ohmoto, 2003;Otake et al, 2007;Yin et al, 2022;Zhao et al, 2019).…”

Nanoscale Mineralogical Characterization of Terrestrial and Extraterrestrial Samples by Transmission Electron Microscopy: A Review

“…As conventional TEM uses electromagnetic lenses to focus the electron beam, magnetic materials can permanently adhere to the lenses, irreparably damaging the system. Therefore, any sample containing magnetic material must be immobilized, for example, by using an oyster grid and FIB method. , In addition, terrestrial and extraterrestrial samples are complicated, so contamination during their preparation must be minimized and can be removed by plasma cleaning. The following four methods are commonly used to prepare TEM specimens from geological samples.…”

“…Classical crystal growth models include layer-by-layer growth (i.e., Kossel–Stranski two-dimensional nucleation growth) and spiral growth mechanism . The application of TEM in recent decades has gradually increased research of nonclassical models of crystal growth such as crystallization of particle attachment (CPA) and amorphous transformation. − Thus, CPA has been found to occurs in supergenic geological processes, high-temperature (e.g., melt) mineralization, and hydrothermal fluid mineralization of shallow crust, suggesting that nonclassical crystal models may occur extensively in various geological processes. Analyzing electron diffraction in TEM has become a mainstream tool for accurately characterizing mineral structures at the nanoscale in the above processes.…”

“…Therefore, any sample containing magnetic material must be immobilized, for example, by using an oyster grid and FIB method. 26,27 In addition, terrestrial and extraterrestrial samples are complicated, so contamination during their preparation must be minimized and can be removed by Terrestrial Samples. Some nanoscale samples are electronically transparent in themselves or at their edges.…”