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A Complex Assemblage of Crystal Habits of Pyrite in the Volcanic Hot Springs from Kamchatka, Russia: Implications for the Mineral Signature of Life on Mars

by Min Tang 1 and Yi-Liang Li 2,*
1
Department of Geology, School of Earth Sciences, Yunnan University, Kunming 650500, China
2
Department of Earth Sciences, The University of Hong Kong, Hong Kong 999077, China
*
Author to whom correspondence should be addressed.
Crystals 2020, 10(6), 535; https://doi.org/10.3390/cryst10060535
Received: 30 April 2020 / Revised: 20 June 2020 / Accepted: 21 June 2020 / Published: 23 June 2020
(This article belongs to the Special Issue Mineralogical Crystallography)
In this study, the crystal habits of pyrite in the volcanic hot springs from Kamchatka, Russia were surveyed using scanning electron microscopy. Pyrite crystals occur either as single euhedral crystals or aggregates with a wide range of crystal sizes and morphological features. Single euhedral crystals, with their sizes ranging from ~200 nm to ~40 µm, exhibit combinations of cubic {100}, octahedral {111}, and pyritohedral {210} and {310} forms. Heterogeneous geochemical microenvironments and the bacterial activities in the long-lived hot springs have mediated the development and good preservation of the complex pyrite crystal habits: irregular, spherulitic, cubic, or octahedral crystals congregating with clay minerals, and nanocrystals attaching to the surface of larger pyrite crystals and other minerals. Spherulitic pyrite crystals are commonly covered by organic matter-rich thin films. The coexistence of various sizes and morphological features of those pyrite crystals indicates the results of secular interactions between the continuous supply of energy and nutritional elements by the hot springs and the microbial communities. We suggest that, instead of a single mineral with unique crystal habits, the continuous deposition of the same mineral with a complex set of crystal habits results from the ever-changing physicochemical conditions with contributions from microbial mediation. View Full-Text
Keywords: Kamchatka; hot springs; pyrite; complexity of crystal habits; Mars Kamchatka; hot springs; pyrite; complexity of crystal habits; Mars
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MDPI and ACS Style

Tang, M.; Li, Y.-L. A Complex Assemblage of Crystal Habits of Pyrite in the Volcanic Hot Springs from Kamchatka, Russia: Implications for the Mineral Signature of Life on Mars. Crystals 2020, 10, 535.

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