『Abstract
Dimensions of plagioclase (An65) crystals
in a polished thin section of naturally weathered 3400 y old Hawaiian
basalt were measured by scanning electron microscopy (in backscattered
electron imaging mode). The three-dimensional shape, size, volume
and surface area of the plagioclase crystals were then estimated
using the method of Morgan and Jerram (2006). The weathering rate
of plagioclase (mass loss divided by initial geometric surface
area during 3400 y) is -12.116 log10 mol
m-2 s-1. This weathering rate represents
a time span (3.4 ka) intermediate between laboratory experimental
timescales and the ages of regoliths in field studies of natural
weathering rates. Weathering rates of the same plagioclase are
recalculated using different assumptions concerning the method
of estimating surface area, including simple geometric surface
area and geometric surface area adjusted for surface roughness.
Varying assumptions about surface area result in variations of
up to two orders of magnitude in rates estimated from the same
basic crystal geometry. The slowest rate estimated here approaches
but does not fall within the range of previously determined field
rates of plagioclase weathering.』
Introduction
Methods
Results
Discussion
Conclusions
References