Jarosite Formation in Weathered Siliceous Chalk in Fontevrault Abbey, Loire Valley, France

Andreas Bauer1, 2 and Bruce Velde1
1 Ecole Normale Supérieure, Departement de Géologie, 24, rue Lhomond, F-75231 Paris Cedex 05, France
2 BRGM, Département Géomatériaux et Géoprocédés, Avenue de Concyr, B.P. 6009, F-45060 Orléans Cedex 2, France

Abstract: Jarosite, a hydrous potassium iron sulphate mineral, has been found as the product of weathering in a silicic chalk building stone of a 13th century abbey at Fontevrault (Maine-et-Loire, France). Destabilization of pyrite and glauconite dispersed in the calcareous stone results in the formation of jarosite. The alteration process is probably of very local origin, within the zone in the building stone at its surface where oxidation occurs during wetting and drying on a cyclical basis. The problem of the incompatibility of highly acidic solutions needed to stabilise jarosite (2.5 < pH) within the highly porous, calcareous silicate rock is not explained at present.

Keywords: Jarosite • silicic chalk • weathering

Mineralogical Magazine; October 1997 v. 61; no. 408; p. 705-711; DOI: 10.1180/minmag.1997.061.408.10
© 1997, The Mineralogical Society
Mineralogical Society (www.minersoc.org)