Discolouration of weathered Lingulid Sandstone in the Forshem church, Västergötland, Sweden

Abstract

185 samples of quartz‐cemented Lingulid Sandstone, mainly from the Forshem church near Kinnekulle in Västergötland (southern Sweden) but also from some local quarries, have been analysed by SEM/EDS and other techniques. The irregular blackish, grey, rust‐brown, orange or yellow patches of discolouration at the rock surface were found to be related to a range of iron minerals, like magnetite, goethite, ferrihydrite, and jarosite. Iron minerals in the rock have been dissolved by rain penetrating into the porous stone. Thereafter the ions have migrated to the surface, where they have formed various coloured iron compounds. Air pollution in the form of acid rain has accelerated their formation. Particles of soot and other dirt are present in so low concentrations that they do not significantly contribute to the colouring.

Nord, A.G., Tronner, K. & Säfström, A., 1994: Discolouration of weathered Lingulid Sandstone in the Forshem church, Västergötland, Sweden. GFF, Vol. 116 (Pt. 2, June), pp. 105–108. Stockholm. ISSN 1103–5897.

Keywords:

• Lingulid Sandstone
• Forshem church
• Kinnekulle
• discolouration
• iron minerals
• iron oxide hydroxides
• jarosite