RT Journal Article
T1 Reaction pathways and textural aspects of the replacement of anhydrite by calcite at 25 °Ck
A1 Roncal-Herrero, Teresa
A1 Astilleros García-Monge, José Manuel
A1 Bots, Pieter
A1 Rodríguez-Blanco, Juan Diego
A1 Prieto, Manuel
A1 Benning, Liane G.
A1 Fernández Díaz, María Lourdes
AB The replacement of sulfate minerals by calcium carbonate polymorphs (carbonation) has important implications in various geological processes occurring in Earth surface environments. In this paper we report the results of an experimental study of the interaction between anhydrite (100), (010), and (001) surfaces and Na2CO3 aqueous solutions under ambient conditions. Carbonation progress was monitored by glancing incidence X‑ray diffraction (GIXRD) and scanning electron microscopy (SEM).We show that the reaction progresses through the dissolution of anhydrite and the simultaneous growth of calcite. The growth of calcite occurs oriented on the three anhydrite cleavage surfaces and its formation is accompanied by minor vaterite. The progress of the carbonation always occurs from the outer-ward to the inner-ward surfaces and its rate depends on the anhydrite surface considered, with the (001) surface being much more reactive than the (010) and (100) surfaces. The thickness of the formed carbonate layer grows linearly with time. The original external shape of the anhydrite crystals and their surface details (e.g., cleavage steps) are preserved during the carbonation reaction. Textural characteristics of the transformed regions, such as the gradation in the size of calcite crystals, from ~2 mm in the outer region to ~17 mm at the calcite-anhydrite interface, the local preservation of calcite crystalographic orientation with respect to anhydrite and the distribution of the microporosity mainly within the carbonate layer without development of any significant gap at the calcite- nhydrite interface. Finally, we compare these results on anhydrite arbonation with those on gypsum carbonation and can explain the differences on the basis of four parameters: (1) the molar volume change involved in the replacement process in each case, (2) the lack/existence of epitactic growth between parent and product phases, (3) the kinetics of dissolution of the different surfaces, and (4) the chemical composition (amount of structural water) of the parent phases.
PB Mineralogical Society of America
SN 0003-004X/17/0006
YR 2017
FD 2017
LK https://hdl.handle.net/20.500.14352/18649
UL https://hdl.handle.net/20.500.14352/18649
LA eng
NO Ministerio de Economía y Competitividad (MINECO)
NO The Marie Curie EU-FP6
NO UK Engineering and Physical Research
DS Docta Complutense
RD 10 abr 2025