MINERALS AND ROCKS

Serpentinite is a rock that consists for the most part of one or more minerals from the serpentine group - phyllosilicate minerals that occur naturally as dense scaly or fibrous aggregates formed by the low-temperature hydrothermal process of olivine or pyroxene mineral exchange in primary ultrabasic rocks. It is a metamorphic rock of green to dark green color, mesh or lattice texture that resembles snake skin, which is why it was named after the Latin word serpens, which means snake. The process by which these changes in minerals occur is called serpentinization, and it takes place most often deep on the seabed on the borders of tectonic plates at temperatures from 200°C to approximately 500°C and under atypical chemical conditions with the presence of water as an oxidizing agent. During serpentinization, the rock absorbs large amounts of water, resulting in an increase in volume, a decrease in density and destruction of the original texture of the rock, and the release of gaseous hydrogen, which plays a significant role in the formation of methane and hydrogen sulfide, together with which it is the main source of energy for deep-sea chemotrophic microorganisms. Serpentinites are very often an integral part of ophiolite zones, rock masses that represent the remnants of the oceanic crust and the upper part of the Earth's mantle, formed in the oceanic environment near mid-ocean ridges, or subduction zones, and have reached land by tectonic movements. It is interesting to mention that the name ophiolite comes from the Greek words ophis and lithos, which mean snake and rock, respectively, due to the fact that it contains serpentinite. In the Banovina area, serpentinites appear as parts of older metamorphic and ultramafic complexes that are associated with the remains of former oceanic lithospheric plates. The area belongs to the Central Dinaric Ophiolite belt that stretches from Banovina through Bosnia and Herzegovina to Serbia and represents part of the ancient Neotethys Ocean that began to form about 250 million years ago by the separation of the supercontinent Pangaea into Laurasia and Gondwana. That ancient ocean disappeared about 50 million years ago when the Indian tectonic plate collided with the Eurasian plate, creating the Himalayan mountain range. Biserka Radanović-Gužvica Croatian Natural History Museum