Precipitation of poorly crystalline antigorite under hydrothermal conditions

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doi: 10.1016/j.gca.2005.02.001
Authors:Gunnarsson, Ingvi; Arnorsson, S.; Jakobsson, S.
Author Affiliations:Primary:
University of Iceland, Institute of Earth Sciences, Reykjavik, Iceland
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 69(11), p.2813-2828. Publisher: Pergamon, Oxford, International. ISSN: 0016-7037
Publication Date:2005
Note:In English. 63 refs.; illus., incl. 5 tables
Summary:Magnesium silicate precipitation experiments were carried out in alkaline solutions in the temperature range 39°C-150°C. Titrations were carried out at room temperature where the pH of an aqueous solution containing magnesium and silica was raised to bring about precipitation of a magnesium silicate. The precipitation of the magnesium silicate was rapid. Equilibrium between the solution and the precipitate was attained in a period of less than one hour up to a month at around 90°C, depending on the initial degree of oversaturation. Relative magnesium and silica depletion in the experimental solutions and IR spectra of the precipitate show that the magnesium silicate resembles poorly developed antigorite (p-antigorite). Values for its solubility constant were obtained and an equation describing its solubility in the temperature interval 0°-200°C calculated. The equation is: log Ksp = 9303/T + 3.283, where T is in K, and it is valid for the following reaction: Mg3Si2O5(OH)4+6H+=3Mg2++2H4SiO40+H2O From thermodynamic data, the solubilities of talc, antigorite, chrysotile, sepiolite, and brucite were calculated in the range 0°C-350°C at Psat. The saturation state of selected surface and ground waters with respect to these minerals and p-antigorite were calculated. In the temperature range 3°C-100°C most of the ground waters are within the limit of error at equilibrium for this phase, but waters of higher temperature are undersaturated. Surface waters are generally undersaturated. It is considered that precipitation of p-antigorite is responsible for the magnesium depletion of surface waters when they seep into the bedrock, and the solubility of this phase controls magnesium concentrations in <100°C ground waters in the basaltic terrain of Iceland. Abstract Copyright (2005) Elsevier, B.V.
Sections:Experimental mineralogy; Geochemistry
Mineral Groups:Sheet silicates
Subjects:Alkalic composition; Alteration; Antigorite; Bedrock; Chemical composition; Chemical ratios; Crystal chemistry; Crystals; Equations; Geochemistry; Ground water; Hydrothermal alteration; ICP mass spectra; Igneous rocks; Infrared spectra; Mass spectra; Mathematical methods; Metasomatism; PH; Precipitation; Saturation; Serpentine group; Sheet silicates; Silicates; Solubility; Solutions; Spectra; Stoichiometry; Temperature; Thermal waters; Thermodynamic properties; Volcanic rocks; X-ray diffraction data; Europe; Iceland; Western Europe
Abstract Numbers:05M/2555
Record ID:2006022285
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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