Weathering of a Basalt by Pertusaria Corallina

Abstract

The weathering phenomena resulting from the encrustation of basalt by Pertusaria corallina have been studied by scanning electron microscopy and a variety of other techniques. The rock consists largely of plagioclase felspar (labradorite) and ferromagnesian minerals, the latter often being replaced by hydrothermally formed ferruginous clay minerals. Lichen weathering results in the extensive etching of the primary rock-forming minerals, particularly labradorite, and in the degradation of the clay minerals to yield a thin ochreous crust of poorly-ordered ferruginous (ferrihydrite) and alumino-silicate materials. These changes are brought about principally by the oxalic acid secreted by the mycobiont, a conclusion supported by observations following experimental mineral alteration.

Fungal weathering of basaltic rocks in a cold oceanic environment (Iceland): comparison between experimental and field observations

“…Here, ribbing is associated with flaking and intense etching of the mineral surface; this can be explained by the weathering model used: A. niger is not in competition with other fungi and the starvation diet compels the fungus to produce more oxalic acid, two factors favouring clear expression of the weathering action of this fungus. Similar features have been experimentally obtained by Jones et al (1980) using similar Aspergillus niger incubated in a glucose solution containing labradorite grains.…”

The weathering action of saxicolous lichens in maritime Antarctica

“…This thallus is also found to include very significant amounts of calcium oxalate (Ca C 2 0 4 2 H 2 0 ) (at 2.5 H20) (weddellite) in the interface, as well as a small amount of calcite (the latter with a peak at 3.02 A). Jones et al (1980) found calcium oxalate monohydrate (CaC204H20) under the thallus of Pertusaria corallina growing on basalt. In a later study of lichens on calcareous rocks, Ascaso et al (1982) found both forms of calcium oxalate monohydrate (whewellite) and dihydrate (weddellite), the latter in very small proportions.…”

“…Such decomposition is carried out by lichen acids and oxalic acid. Jones et al (1980) demonstrated the formation of calcium oxalate in the interface between basalt and Pertusaria corallina, and the formation of manganese oxalate by the same lichen growing on a mineral containing manganese (Wilson and Jones 1984). Glushinskite (magnesium oxalate) was also observed in the serpentinite interface colonized by Lecanora atra .…”

The role of ectomycorrhizal fungi in calcareous soil tolerance by "symbiocalcicole" woody plants

“…While mycorrhizal fungi are more or less tolerant to calcareous soils, depending on their ecological origin, they tolerate extremely high concentrations of calcium ions (Lapeyrie et al, 1982 (Jones et al, 1980;Jones and Wilson, 1985). Oxalic acid is an acid as well as chelating agent and after excretion in the soil it is particularly efficient in minerals alteration (Robert et al, 1979).…”