A LONG-TERM NATURAL ANALOGUE FOR RADIOACTIVE WASTE REPOSITORIES? MINERALOGY AND CHEMISTRY OF A VOLKONSKOITE (CR-RICH SMECTITE) IN TRAVERTINE DEPOSITS FROM CENTRAL JORDAN

摘要

In Quaternary travertine deposits of central Jordan emerald and green clays were noticed filling cavities and fractures, believed to be volkonskoite. Foord et al. (1987) defines volkonskoite as a dioctahedral member of the smectite group dominated by Cr in the octahedral sheet, meaning more than one of the two octahedral sites should be occupied by Cr. Smectites with lesser Cr (e.g. Cr_2O_3 typically less than 15%) would be properly termed chromium montmorillonite. The travertine deposits precipitated from warm hyperalkaline groundwater (pH = 12.5) at the interface between bituminous marl and marble making it a potential long-term natural analogue of carbonation and remobilization of alumino-silicates in cement barriers for radioactive waste repositories.