ultramafic rocks are essentially constituted by silicates of magnesium: forsterite, and/or diopside-enstatite; who’s the most common hydrothermal alteration are the serpentinization. to bou azzer, the serpentinisation affected almost all of the ultrabasic rocks. among the phenomena bound to the serpentinisation observed on the ground, we distinguish the magnesium deposits (carbonated serpentini...