Geoscience Reference
In-Depth Information
Fig. 1.4 Example of a thin section sampled from a weathered granite in the Pilat massif
(Loire, France). The section represents 2 cm × 3 cm. The matrix is composed of primary min-
erals such as quartz and feldspars (2) and dark micas (3). A crack (1) shows that pedological
weathering has begun. The walls are lined with clay coatings that have been deposited in
successive layers (4). Photo : author.
1.2.4 Mass-balance Analysis
For understanding the genesis of a horizon of a soil, it is often important
to calculate the quantity of material that has been exported, for example
of iron, aluminium or silicon. Let us examine the methods (Legros 1982;
Driese et al. 2000) taking as example the losses of iron, whereby we
avoid having to introduce an index showing that every element could
be concerned.
The notations are chosen in such a way that they can directly be
used in elaboration of a computer program in C, for example. Let
￿ da ( r ) be the density of the parent material or reference horizon
and da ( i ) that of the horizon i studied,
￿ vol ( i ) be the present volume of the horizon i studied,
￿ volor ( i ) be the initial volume of horizon i (it could be different
from the present volume because of gains or loss of material),
￿ MI ( r ) be the quantity in the parent material of a mineral totally
resistant to weathering and MI ( i ) the quantity of the same
mineral in the horizon i studied (in g per 100 g),
￿ Fe ( r ) be the iron content of the parent material and Fe ( i ) that of
horizon i studied, also expressed in g per 100 g.
Search WWH ::




Custom Search