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Open AccessArticle

Brucite-Aragonite Precipitates as Weathering Products of Historic Non-MgO-Based Geomaterials

1
Spanish Geological Survey (IGME), Calle Ríos Rosas, 23, 28003 Madrid, Spain
2
Department of Earth Sciences and the Environment, University of Alicante, Apdo. Correos 99, San Vicente del Raspeig, 03080 Alicante, Spain
3
Department of Environmental and Land Sciences and Earth Sciences. Univeristy of Milano-Bicocca, 20126 Milan, Italy
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(7), 599; https://doi.org/10.3390/min10070599
Received: 10 June 2020 / Revised: 22 June 2020 / Accepted: 25 June 2020 / Published: 30 June 2020
(This article belongs to the Special Issue Minerals and Other Phases in Constructional Geomaterials)
This paper analyses the mineralogical composition, texture, and structure of a stalactite sampled from the city-wall storerooms of the Nueva Tabarca fortress (southeast Spain). This speleothem presents an uncommon mineral assemblage: aragonite, brucite, gypsum, silica, and halite. Internally, it shows complex structure: (1) a central soda-straw composed by aragonite; (2) an external puff-pastry cone-crust formed preferentially by aragonite and brucite; and (3) an internal branching of coralloids, showing a subtle layering between brucite and aragonite. Gypsum, halite, and silica locate in the outer coating of the cone-crust. The sequent mineral precipitation sequence has been established: aragonite > brucite > gypsum/silica > halite. Speleothem formation is directly related to the chemical weathering of the rocks and mortars used as building materials of the city-wall. Brucite precipitates has been always linked to the presence of MgO-based geomaterials. However, the lack of these compounds as building materials in Nueva Tabarca fortress makes this investigation a unique example of brucite precipitation. PHREEQC calculations showed that interaction between pore waters and the minerals of mortar aggregates (dolomite, pyroxene, and amphibole) leads to rich-magnesium solutions. Evaporation modelling of lixiviated waters describes the precipitation of the mineral assemblage of the brucite-aragonite speleothems. View Full-Text
Keywords: brucite; X-ray computed tomography; speleothem; stalactite; geochemistry brucite; X-ray computed tomography; speleothem; stalactite; geochemistry
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Martínez-Martínez, J.; Benavente, D.; Fusi, N.; Cañaveras, J.C. Brucite-Aragonite Precipitates as Weathering Products of Historic Non-MgO-Based Geomaterials. Minerals 2020, 10, 599.

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