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Open AccessArticle

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

Spanish Geological Survey (IGME), Calle Ríos Rosas, 23, 28003 Madrid, Spain
Department of Earth Sciences and the Environment, University of Alicante, Apdo. Correos 99, San Vicente del Raspeig, 03080 Alicante, Spain
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;
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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