『Abstract
Biophysical and biogeochemical weathering of amphibole syenite
associated with the Stettin complex near Wausau, Wisconsin, has
been examined by HRTEM, WDS, LM, and XRD. The rock consists of
microperthitic feldspar, ferriannite, quartz, and ferrohastingsite.
Crustose saxicolous lichens, Rhizocarpon grande and Porpidea
albocaerulescens, penetrate the rock surface to a depth of
10 mm. within the intact rock, amphibole surfaces along hyphae-filled
cracks are highly corroded. Fungal hyphae exploit grain boundaries,
cleavages, and cracks to gain access to mineral surfaces, resulting
in accumulations of cleavage-bound mineral fragments as small
as 5 μm within the lower thallus. Bacterial microcolonies are
common and all mineral surfaces are completely coated in extracellular
acidic mucopolysaccharides from fungal and bacterial sources.
In the cases of amphibole, quartz, and feldspar, dissolution does
not appear to involve pervasive leaching, for even the smallest
mineral fragments retain their chemical and structural identity.
Biotite directly in contact with the lichen thallus is intimately
interpenetrated by fungal hyphae growing along (001) cleavages
and is partially converted to vermiculite. No siliceous relics
have been identified. Biologically mediated weathering involves
a complex dissolution/selective transport/recrystallization mechanism
occurring within the acidic extracellular gels coating all mineral
surfaces. A specialized weathering microenvironment around each
mineral grain initially produces minute phyllosilicate crystallites.
A rind of clay minerals forms around the dissolving parent phase,
eventually culminating in abundant 5-10μm diameter polymer-bound
aggregates of face-to-face oriented clay minerals of homogeneous
composition.
Physiochemical weathering of ferrohastingsite produces topotactically
oriented smectite and goethite. The cleavage-controlled reaction
is neither isochemical nor isovolumetric.』
1. Introduction
2. Materials and methods
3. Results
3.1. Unweathered silicates
3.2. Physiochemical and biologically mediated weathering
3.2.1. Ferrohastingsite
3.2.2. Ferriannite
3.2.3. Quartz
3.2.4. Feldspar
4. Discussion and conclusions
Acknowledgements
References