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Article

Unusual Perforations in Phlogopite Crystals from Caldara di Manziana (Italy) Caused by Sulphuric Acid Generated by Microbial Oxidation of H2S Emanations

1
Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
2
Institute for Biological Systems, Council of National Research of Italy (CNR), Area della Ricerca di Roma 1, via Salaria Km 29,300, Monterotondo, 00015 Rome, Italy
3
Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
*
Author to whom correspondence should be addressed.
Academic Editor: Jinwook Kim
Received: 19 April 2021 / Revised: 15 May 2021 / Accepted: 18 May 2021 / Published: 20 May 2021
(This article belongs to the Special Issue Clay Minerals–Life Interplay)
Phlogopite flakes strewn on the soil of Caldara di Manziana (Italy) display multiple minute perforations. The site is a caldera linked to recent volcanism (90 ka to 0.8 Ma) with present emanations of CO2 (~150 t d−1) and H2S (~2.55 t d−1). Stereomicroscopy and SEM–EDX observation of the phlogopite crystals shows holes and depressions <200 µm to 2 mm across. They are circular, pseudo-hexagonal, or irregular. Within the depressions, there are deposits of phlogopite alteration products consistent with a sulphuric acid attack, showing loss of Mg and K. Some are thin and homogeneous; others are thick, irregular, and chemically heterogeneous, including plates, flakes, tubes of Fe-beidellite or Fe-bearing halloysite, silica, Fe oxides, and gypsum. Areas of phlogopite surface are also altered. Sulphuric acid is produced from the H2S gas by the mediation of sulphur-oxidizing bacteria. Pseudo-hexagonal perforations are interpreted to result from slow acid attack with dissolution controlled by phlogopite crystal symmetry. Some depressions developed surrounding films of pseudo-hexagonal shape, interpreted as jarosite crystallizing radially outwards from the depressions. This style of acid attack is possibly promoted by local high humidity and precipitation that generate long-lived water droplets and films on mineral surfaces where sulphuric acid is active for prolonged times. View Full-Text
Keywords: acid alteration; Caldara di Manziana; phlogopite; sulphur-oxidizing bacteria acid alteration; Caldara di Manziana; phlogopite; sulphur-oxidizing bacteria
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MDPI and ACS Style

Pinzari, F.; Cuadros, J. Unusual Perforations in Phlogopite Crystals from Caldara di Manziana (Italy) Caused by Sulphuric Acid Generated by Microbial Oxidation of H2S Emanations. Minerals 2021, 11, 547. https://0-doi-org.brum.beds.ac.uk/10.3390/min11050547

AMA Style

Pinzari F, Cuadros J. Unusual Perforations in Phlogopite Crystals from Caldara di Manziana (Italy) Caused by Sulphuric Acid Generated by Microbial Oxidation of H2S Emanations. Minerals. 2021; 11(5):547. https://0-doi-org.brum.beds.ac.uk/10.3390/min11050547

Chicago/Turabian Style

Pinzari, Flavia, and Javier Cuadros. 2021. "Unusual Perforations in Phlogopite Crystals from Caldara di Manziana (Italy) Caused by Sulphuric Acid Generated by Microbial Oxidation of H2S Emanations" Minerals 11, no. 5: 547. https://0-doi-org.brum.beds.ac.uk/10.3390/min11050547

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