chloritizzazione

Chloritization is a metamorphic process that transforms existing minerals, typically mafic silicates like pyroxenes and amphiboles, into minerals of the chlorite group. This alteration occurs under low-grade metamorphic conditions, generally at temperatures ranging from 200 to 400 degrees Celsius and pressures that are not exceptionally high. The key chemical agent in chloritization is water, often accompanied by a source of oxygen and sometimes other dissolved ions.

The process involves the hydration and oxidation of the parent minerals. For example, olivine and pyroxene, common in basaltic rocks, can undergo chloritization to form chlorite, often alongside other secondary minerals like quartz, epidote, or actinolite. Amphiboles are also readily converted to chlorite. The resulting rocks are often greenish in color due to the presence of chlorite, which typically has a green hue.

Chloritization is a common feature in many metamorphic terrains, particularly those associated with regional metamorphism of volcanic and intrusive igneous rocks, as well as in hydrothermal alteration zones. It is a significant indicator of the physical and chemical conditions under which a rock has been metamorphosed. The extent of chloritization can provide clues about the intensity and duration of hydrothermal activity or metamorphic events.