Calcisols and other Soils on Carbonate-Bearing and Sulphate-Bearing Materials - Major Soil Groups of the World - page 225

Sometimes the substrata of calcareous crusts are composed of acid
rocks. In such cases the rock often contains a little calcium (for example,
granite with plagioclases) and the Ca ++ ions released by weathering can
combine with dissolved CO 2 to precipitate as CaCO 3 . This evolution
(appearance of lime in granite-derived soils) occurs in very dry climates.
The process can be important on the footslope, where calcium carbonate
is concentrated. It could be induced by trees and mushrooms: formation
of oxalate later transformed to carbonate by microorganisms (Cailleau
et al. 2005).
Calcium is often carried by wind also. In particular, glaciations have
led to the appearance of large denuded areas (in front of the glaciers
and also on the seashore when the ocean levels drop). This phenomenon
promoted deflation. In some cases, loesses are easily identified. In other
cases the sprinkling of calcareous silts is more subtle, but it assumes
importance on acid materials and on those that leave little weathering
residue, for example hard pure limestones (Pochon 1978; Havlicek and
Gobat 1996). Some authors feel that allochtony is responsible for one-half
or three-quarters of the total fine earth in the soils of the Alps!
Some crusts can form in drained calcareous muds. In other words,
they have lacustrine or coastal origin: southern Australia, Tunisia, etc.
They have specific features (Milnes 1992; Fu et al. 2004).

Sometimes spectacular phenomena are observed: schists cut up into
small compartments by broad veins of calcite, isolated granite balls
in a calcareous gangue, quartzites corroded and appearing as if eaten
by carbonates. In short, CaCO 3 can replace all minerals (Paquet and
Ruellan 1993; Ruellan 1984): quartz, micas, feldspars, clay minerals,
hydroxides…
Let us try to explain this. In the medium on the way to crusting,
porosity diminishes and the additions of CO 2 are small, especially
during periods of saturation with water. In these conditions, we have
seen that the pH rises to 9.9. Actually it rises further because of the
presence of other ions, sodium in particular. A value of 11 is possible.
The solubility of silica increases (Millot 1977; Halitim et al . 1983; Ruellan
1984). Quartz and silicates are dissolved. They leave voids thanks to
which the pores are not closed, thus permitting calcium-rich solutions
to continue penetrating (in the wet season) and then for CaCO 3 to

Epigenesis