Formation of Melanterite From Marcasite: Insights Into Martian Transient Wet Conditions

Document Type

Article

Publication Date

6-2-2026

Department

Department of Geological and Mining Engineering and Sciences

Abstract

This study reports the first occurrence of melanterite (Fe2+SO4·7H2O), a secondary hydrous sulfate mineral, in Peninsular India and examines its formation through the oxidative weathering of marcasite associated with lignite in Neyveli, Tamil Nadu. The marcasite was exposed to normal atmospheric conditions, and melanterite was formed within 23 days via oxidative weathering. Melanterite occurs as a yellow, prismatic to fibrous, translucent crystal, either as individual fibers or clusters. Though melanterite is mineralogically characterized through different techniques like X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy, and electron probe microanalysis (EPMA), the results obtained from EPMA [(Fe0.839 Cu0.000355 Zn0.000466 Ni0.000545) SO4·7H2O] closely match the composition of standard melanterite. Fourier Transform Infrared spectroscopy identified key vibrational peaks for sulfates (450–480 cm−1) and water molecules (1,544–1,650 cm−1), while laser Raman spectroscopy provided evidence for the characteristic vibration of melanterite at 976 cm−1. Hyperspectral analysis also discerned the characteristic Fe2+ peak (0.45–0.9 μm) of melanterite. A spectrum, comparable to that of melanterite, obtained through Compact Reconnaissance Imaging Spectrometer for Mars data from the Ceti Mensa region on Mars, where it is associated with a polysulfate deposit. Since melanterite forms under acidic and oxidizing conditions in low moisture, its occurrence can provide insights into the environmental conditions under which sulfate forms. Thus, this study can provide insights into studying transient wet conditions on Mars.

Publication Title

Journal of Geophysical Research Planets

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