Composition and morphology of ferromanganese coatings on glacial erratics in Lydonia Canyon, United States East Coast

Ferromanganese coatings have been found on glacial erratics in Lydonia Canyon, off the United States northeastern coast. The coatings, which are about 17 μm thick, consist of an outer manganese-rich layer which covers the top of the erratic, a middle transitional layer, and an internal iron-rich layer that encircles the entire surface of the erratic. Chemical analyses of the coatings, when compared with similar data on abyssal marine ferromanganese deposits, reveal comparable Mn/Fe ratios, higher P and Ti concentrations, and an order of magnitude less of Co, Ni, Cu, and most other metals. A comparison of the Lydonia Canyon coatings with desert varnishes reveals obvious chemical, mineralogical, and morphological differences.