In Ios there are transformed rocks, mainly gneisses and schists. Its largest part is occupied by a large block of granite. The granite of Ios was dated with the method of uranium/lead (U/Pb) in the Upper Carboniferous (300 million years). It appears to be gneiss-like, since it suffered from Alpine metamorphism later and it shows intense schist formation. Large blocks of this granite surround the port of Ios and dominate the region with the dark green colors which are due to the chlorite.