As previously seen, after 14 h degradation, the
grains have different alteration stages. Fig. 26 shows a
grain which has not reacted. It presents a uniform
appearance. The line profile by microanalysis on this
grain shows a very small potassium content and a lack
of calcium inside the grain (these values are near the
detection limits). At the surface, the silicon content
falls at the boundary of the grain and a small quantity
of potassium and calcium is detected. On the other
hand, on a grain-beginning alteration, potassium is
detected when the line profile goes through pseudomorphosis
zones (Fig. 27). The amount of calcium
remains negligible. This result shows that the potas