『Abstract
The mechanisms by which coatings develop on weathered grain surfaces,
and their potential impact on rates of fluid-mineral interaction,
have been investigated by examining feldspars from a 1.1 ky old
soil in the Glen Feshie chronosequence, Scottish highlands. Using
the focused ion beam technique, electron-transparent foils for
characterization by transmission electron microscopy were cut
from selected parts of grain surfaces. Some parts were bare whereas
others had accumulations, a few micrometers thick, of weathering
products, often mixed with mineral and microbial debris. Feldspar
exposed at bare grain surfaces is crystalline throughout and so
there is no evidence for the presence of the amorphous ‘leached
layers’ that typically form in acid-dissolution experiments and
have been described from some natural weathering contexts. The
weathering products comprise sub-μm thick crystallites of an Fe-K
aluminosilicate, probably smectite, that have grown within an
amorphous and probably organic-rich matrix. There is also evidence
for crystallization of clays having been mediated by fungal hyphae.
Coatings formed within Glen Feshie soils after 〜1.1 ky are insufficiently
continuous or impermeable to slow rates of fluid-feldspar reactions,
but provide valuable insights into the complex weathering microenvironments
on debris and microbe-covered mineral surfaces.
Keywords: alkali feldspar; TEM; smectite; weathering.』
Introduction
Methodology
Soils and their mineralogy
SEM, FIB and TEM
Results
Bare grain surfaces
Coated grain surfaces
Discussion
Conclusions
Acknowledgements
References