Desert varnish in Antarctica: A nuclear microprobe and backscattered 57Fe Mössbauer spectroscopic study

Occurrence and Constitution of Natural and Synthetic Ferrihydrite, a Widespread Iron Oxyhydroxide

“…Ferrihydrite typically forms where oxidation of Fe(II) is rapid, and thus it is perhaps not surprising that the first reported occurrence of ferrihydrite in soils was for weathered crusts on basalts in Hawaii − in loess, as the precursor to hematite in rubified (hematitic) soils, in a peat bog, in bog iron, in soil concretions and hardpan, in oxidized surface layers of saline sulfidic soils of Australia, and as the oxidized coatings on diabase and sandstone in Antarctica . Numerous additional references to the presence of ferrihydrite in soils are given in the review papers by Childs 8 and Schwertmann, , who cite publications on well-documented occurrences in hydromorphic (gley) soils, in placic horizons, in podzols, , in Spodosols and Spodosol-like soils, in soils derived from volcanic ash and tephra, in rice-paddy soils, and in iron pans.…”

“…51 Ferrihydrite has since been detected as an important constituent in Spodosols, [52][53][54] in loess, 55 as the precursor to hematite in rubified (hematitic) soils, 56 in a peat bog, 57 in bog iron, 58 in soil concretions 59 and hardpan, 60 in oxidized surface layers of saline sulfidic soils of Australia, 61 and as the oxidized coatings on diabase and sandstone in Antarctica. 62 Numerous additional references to the presence of ferrihydrite in soils are given in the review papers by Childs 8 and Schwertmann, 12,63 who cite publications on welldocumented occurrences in hydromorphic (gley) soils, in placic horizons, 64 in podzols, 65,66 in Spodosols and Spodosol-like soils, in soils derived from volcanic ash and tephra, 67 in rice-paddy soils, 68 and in iron pans. Childs 8 noted that long periods of weathering usually lead to the formation of goethite and hematite, and that the emerging general impression is that ferrihydrite is a common component of...soils undergoing rapid early weathering, of soils containing soluble silicate or organic materials that inhibit the formation of more crystalline iron oxides (and hence stabilize ferrihydrite), and of soils that are subject to periodic reduction and oxidation (including paddy soils).…”

The weathering of granodiorite porphyry in the thiel mountains, inland antarctica

“…Rock varnish is generally Fe-and Mn-rich, but in Antarctica, varnish that is both Fe-and Mn-rich has rarely been found (Dorn et al 1992). Most varnish found in Antarctica does not contain manganese; it is of the Fe-rich but Mn-poor type (Kelly and Zumberge 1961;Glasby et al 1981;Johnston et al 1984). EDS analysis did not detect manga-nese, showing that the rock varnish in this study is in fact Fe-rich but Mn-poor.…”

“…Most varnish found in Antarctica does not contain manganese; it is of the Fe-rich but Mn-poor type (Kelly and Zumberge 1961;Glasby et al 1981;Johnston et al 1984). EDS analysis did not detect manganese, showing that the rock varnish in this study is in fact Fe-rich but Mn-poor.…”

“…Sulfate (SO 4 2-) advances oxidation, hence sulfur is important in oxidation. The sulfur in rock varnish in Antarctica is originally derived from volcanic gas (Kelly and Zumberge 1961), sea-spray (Keys and Williams 1981), windblown inorganic salts (Johnston et al 1984), glacier water (Hayashi and Miura 1989), or other sources. Our rock sample includes pyrite (FeS 2 ), but only in a small amount.…”