Rock fragments with dark coatings in slope deposits of the Famenne region, southern Belgium

Quaternary slope deposits near the Lesse river in the Famenne region, south Belgium, contain scattered rounded rock fragments (5-15 cm diameter) that are typically characterized by a dark coating or patina. This dark surface resembles rock varnish occurrences. To establish the nature of the coatings, chemical, mineralogical and petrographical analyses were performed. The coatings are essentially Fe/Mn oxide features, developed as surface deposits on the rock fragments with associated impregnation of the rock substrate. The Fe/Mn compounds are amorphous or at least poorly crystalline. The coati... Mehr ...