The first stage of the transformation of a rock into a soil is represented by the physical process of fragmentation.
This process is clearly demonstrated when observing
a soil thin section in the microscope. The mineral grains are
cracked to a greater or lesser extent. The disintegration of the
rock produces a wide system of cracks (at the beginning very fine,
with adjustable walls) and separates the grains individually,
which will have very different sizes. The cracks are shown as
colourless lines (with different thicknesses) with only the polarizer
and they appear black when the analyser is placed.