FUNGAL QUARTZ WEATHERING AND IRON CRYSTALLITE FORMATION IN AN ALPINE ENVIRONMENT, PIZ-ALV, SWITZERLAND

A quartzite lens occurring within the Triassic Hauptdolomite Formation of the Lower Austroalpine Bernina Nappe near Piz Alv, Switzerland, ha s been heavily eroded and altered by fungal dissolution of SiO2 and su bsequent precipitation of iron crystallites. Preliminary studies show that fungal hyphae of the class Basidiomycetes occur most abundantly a long mechanically weak zones in the quartzite. Occasionally, hyphae oc cur within quartz crystals, into which they bored subperpendicularly f rom the quartz surface by dissolving SiO2. The hyphae are approximatel y 3-9 mu m in diameter and up to 300 mu m long. They commonly consist of a hollow central part and an encrusted rim. The encrustations consi st mostly of spherical bodies forming a chain-like structure along the former hyphae. They show a variety of crystal structures and consist mainly of needle-shaped goethite (FeOOH) with lesser amounts of platy hematite (Fe2O3) arranged in rosettes. These iron phases account for t he conspicuous yellow colour of the quartzite lens. The variety and ar rangement of the spherical iron crystallites along fungal hyphae show a striking similarity to calcium oxalate crystals arranged along labor atory grown fungal hyphae. Such calcium oxalates form as a by-product of fungal secretion of oxalic acid in the presence of calcium ions. Th us, we assume that quartz dissolution and iron crystallite formation i n the investigated quartzites is associated with the presence of oxali c acid secreted by the fungal hyphae.