Abstract

Chemical and mineralogical analyses of a profile derived from dunite suggested that the serpentine transformed into chlorite and montmorillonite. The parent dunite was formed by lizardite plus clino-chrysotile mainly, but also contained brucite and magnetite. Brucite was rapidly dissolved in the early stage of weathering. Thereafter, there was a further loss of MgO and constitution H2O and a corresponding increase in SiO2. In the clay fraction, serpentine transformed, through interstratified minerals, into montmorillonite and chlorite (part of which was made of Al-montmorillonite).Feldspar, hornblende, and quartz were restricted to some fractions in the upper part of the profile, and this suggests that the deposit had not been extensively reworked by the glaciers.The weathering conditions at the site favored the formation of an Orthic Melanic Brunisol.

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