^1,2E. L. Cardarelli, ³T. M. Present, ⁴P. M. Vasconcelos, ⁵L. C. Kah, ^3,6C. Swindle, ³S. Bhattacharjee, ³K. Farley
Journal of Geophysical Research: Planets, 131, e2026JE009660 Open Access
Link to Article [DOI: 10.1029/2026JE009660]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
³Division of Geologic and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
⁴The University of Queensland, Brisbane, QLD, Australia
⁵Department of Earth, Environmental and Planetary Sciences, University of Tennessee, Knoxville, TN, USA
⁶Department of Materials Science and Engineering, University of California, Los Angeles, CA, USA
Published by arrangement with John Wiley & Sons

Magnesite (MgCO₃) is a magnesium (Mg) carbonate mineral that records the aqueous environmental conditions of its formation. On Earth, magnesite forms in metamorphic, diagenetic or pedogenic environments, and distinguishing between these environments is critical for understanding the fluid chemistry during magnesite precipitation. Mg carbonates have been observed across the Nili Fossae region on Mars and in Jezero crater by orbital spectroscopy as well as in situ by the Perseverance rover. Rover acquired core samples with Mg carbonates may provide constraints on the chemical conditions of the ancient aqueous environments of Jezero crater, and may also be an important target for the preservation of potential biosignatures. This work explores magnesite phases found in Vertisols of the Kunwarara Mine, Australia, as a potential analog environment for magnesite on Mars. We document the principal microtextures, mineralogical context, and elemental compositions. We investigate the processes involved in the formation and diagenesis of magnesite nodules and a magnecrete. Kunwarara hosted magnesite shows complex textural relationships at the outcrop scale, and these relationships extend down to the nanoscale in samples that were collected along a depth profile. By characterizing textural and chemical variations in magnesite at different scales, this work reveals a continuum between diagenetic and pedogenic magnesites. It illustrates that diagenetic reactions produce magnesite from ascending Mg²⁺-rich groundwater interacting with detrital phases; groundwater interaction with descending meteoric solutions result in the conversion of magnesite into authigenic dolomite. Overall, this work shows how the superposition of textures and elemental compositions permits reconstruction of pedogenic processes leading to magnesite authigenesis.