Olivine mineral replacement by serpentine is one major alteration
reaction of oceanic hydrothermalism. In the present experimental study,
olivine grains were replaced by chrysotile and brucite under high
alkaline conditions. In our study, olivine replacement implied a spatial
and temporal coupling of dissolution and precipitation reactions at the
interface between olivine and chrysotile-brucite minerals. Coupled
dissolution-precipitation led to the alteration of starting olivine
grains (so-called primary or parent mineral) to a porous mineral
assemblage of chrysotile and brucite with preservation of the initial
olivine morphology. This mineral replacement reaction of olivine
(serpentinization) has been characterized using XRD, FESEM and FTIR
measurements. Moreover, a simple and novel method is here proposed to
quantify the mineral replacement rate (or serpentinization rate) of
olivine using thermogravimetric (TG) and differential TG (DTG) analyses.
Serpentinization extent depends on the grain size: it is complete after
30 days of reaction for the smallest olivine grains (< 30 mu m), after
90 days of reaction for the intermediate olivine grains (30 mu m-56 mu
m). For the largest fraction (56-150 mu m), 55% of serpentinization
extent was reached after 90 days. Based on the fitting of the
serpentinization extent versus time (t) using a kinetic
pseudo-second-order model, the serpentinization rates vary from 3.6 x
10(-6) s(-1) to 1.4 x 10(-7) s(-1) depending on the olivine grain size.
An additional correlation between FTIR spectra analysis and TG
measurements is proposed. The mineral replacement reactions frequently
observed in natural alteration processes could be a powerful synthesis
route to design new porous and/or nanostructured materials. (C) 2012
Elsevier B.V. All rights reserved.