Influence of temperature and Cl on the hydrothermal replacement of calcite by apatite and the development of porous microstructures

Jonas, Laura; John, Timm; Putnis, Andrew

doi:10.2138/am.2013.4288

Cited by 16 publications

(13 citation statements)

References 29 publications

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“…This process might have an impact on the permeability of the rim, justifying the slower replacement rates for bigger replacement rims. Jonas et al (2013) found that changes in the porosity during the replacement of calcite by apatite resulted in kinetic data that could not be successfully fitted to Avrami rate equations. The smaller difference in molar volumes, and hence porosity, and the higher reaction temperatures resulted in more rapid textural equilibration in the reaction rims and hence greater variation in porosity.…”

Section: Replacement Reaction Mechanismmentioning

confidence: 99%

“…For example, calcite (CaCO 3 ) may be replaced by other carbonates such as dolomite or siderite (Pearce et al, 2013) or may form other calcium compounds when in contact with appropriate solutions. For example, calcite in contact with PO 4 -bearing solutions is easily replaced by apatite, Ca-phosphate (Yoshimura et al 2004;Kasioptas et al 2011;Jonas et al 2013Jonas et al , 2014Pedrosa et al 2016).…”

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confidence: 99%

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The replacement of a carbonate rock by fluorite: Kinetics and microstructure

Pedrosa

Boeck

Putnis

et al. 2017

American Mineralogist

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Understanding the mechanism and kinetics of the replacement of carbonates by fluorite has application in Earth sciences and engineering. Samples of Carrara marble were reacted with an ammonium fluoride (NH 4 F) solution for different reaction times and temperatures. The microstructure of the product phase (fluorite) was analyzed using SEM. The kinetics of replacement was monitored using Rietveld analysis of X-ray powder diffraction patterns of the products. After reaction, all samples preserved their size and external morphology (a pseudomorphic replacement). The grain boundaries of the original marble were preserved although each calcite grain was replaced by multiple fine crystals of fluorite creating inter-crystal porosity. The empirical activation energy E a (kJ/mol) of the replacement reaction was determined by both model-fitting and model-free methods. The isoconversional method yielded an empirical activation energy of 41 kJ/mol, and a statistical approach applied to the modelfitting method revealed that the replacement of Carrara marble by fluorite is better fitted to a diffusion-controlled process. These results suggest that the replacement reaction is dependent on the ion diffusion rate in the fluid phase through the newly formed porosity.

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Section: Replacement Reaction Mechanismmentioning

confidence: 99%

mentioning

confidence: 99%

The replacement of a carbonate rock by fluorite: Kinetics and microstructure

Pedrosa

Boeck

Putnis

et al. 2017

American Mineralogist

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“…In many cases they occur at laboratory time scales under hydrothermal conditions, meaning that they are more effi cient than diffusion-controlled reactions at geologic conditions. The microstructures developed during dissolution-precipitation reactions are affected not only by fl uid composition (Jonas et al, 2013) and mineral solubility (Pollok et al, 2011), but also by factors such as pH (Xia et al, 2009). Existing experimental studies of mineral replacement are mainly focused on replacement reactions involving either replacement of one phase by another or alteration of one end member of a solid solution to an intermediate composition.…”

Section: Introductionmentioning

confidence: 99%

Complex mineral zoning patterns caused by ultra-local equilibrium at reaction interfaces

Borg

Liu

Pearce

et al. 2014

Geology

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“…Carrara marble is an ideal experimental material because it is a relatively pure calcium carbonate (calcite) rock with regular grain size (average 200 μm), and the pseudomorphic replacement of calcite by apatite has been previously demonstrated (e.g. Ames, 1959Ames, , 1961Kasioptas et al, 2008Kasioptas et al, , 2010Kasioptas et al, , 2011Jonas et al, 2013Jonas et al, , 2014Borg et al, 2014).…”

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confidence: 99%

The pseudomorphic replacement of marble by apatite: The role of fluid composition

Pedrosa

Putnis

2016

Chemical Geology

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The replacement of a natural carbonate rock (Carrara marble) by apatite was used as a model to study the role of fluid chemistry in replacement reactions, focusing on the mineralogy, chemical composition, and porosity of the replacementproduct.Carrara marble was reacted with ammonium phosphate solutions ((NH 4) 2 HPO 4), in the presence and absence of four salt solutions (NH 4 Cl, NaCl, NH 4 F, and NaF) at different ionic strengths, at 200°C and autogenous pressure. The replacement products were analysed usingpowder X-ray diffraction,Scanning electron microscopy (SEM), electron microprobe analysis(EMPA), and Raman spectroscopy. The reaction in all samples resulted in pseudomorphic replacements and shared the characteristics of an interface-coupled dissolution-precipitation mechanism. Increasing theionic strength of the phosphatefluid increased the replacement rates. With a fixedconcentration of phosphate, replacement rates were reduced with the addition of NH 4 Cl and NaCland increased significantly with the addition of NaF and NH 4 F. The addition of different salts resulted in specific porosity structures resulting from the formation of different phosphate phases. Chlorine-containing fluids showed a higher degree of fluid percolation through grain boundaries. This study illustrates the significant impact that small differences in solvent composition can have in the progress of replacement reactions, the nature of the products and the resultant porosity.

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Influence of temperature and Cl on the hydrothermal replacement of calcite by apatite and the development of porous microstructures

Cited by 16 publications

References 29 publications

The replacement of a carbonate rock by fluorite: Kinetics and microstructure

The replacement of a carbonate rock by fluorite: Kinetics and microstructure

Complex mineral zoning patterns caused by ultra-local equilibrium at reaction interfaces

The pseudomorphic replacement of marble by apatite: The role of fluid composition

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