Kimolos, Milos and the smaller islands that surround them belong to the Aegean volcanic arc and consist mainly of acidic volcanic rocks. In some places, the pre-volcanic bedrock can be observed. Large areas of Kimolos are covered by
tuffs and the volcanic activity can be obvious from the hot springs, existence of a notable geothermal field, the characteristic landscape and strange landforms. The island is also rich in minerals of the
silica group and in significant industrial minerals.
Theodore Bent in December 1883 noted “a sort of white porous stone, easy to cut and much prized for building, for it hardens with time; it is the old 'terra Kimolia', out of which the ancients made
Fuller's earth.” One of the most famous geologic formations on Kimolos is
Skiadi. Skiadi is a huge mushroom-shaped stone that dominates the middle of a small valley in the interior of the island. It is created by a process called
ablation, in which the dust carried by the wind continuously scratches the rock, eroding the softer layers at the bottom much more than the harder layers at the top. Through centuries, the stone has been shaped into a characteristic, unique form. ==Residents==