As Kimolos is located in the outer zone of the Aegean’s volcanic arc, the local volcanic activity may have calmed over the centuries but left visible traces on the island, such as hot springs and irregular geological formations which make up incredible landscapes of rare beauty. A large surface of the island is covered by tuffs. This is a light rock, usually cut in rectangular parallelepiped pieces, the “poria”, used as a building material. It was once a significant source of income for the residents since it was transported by boats over long distances in and out of Greece. There are many important industrial minerals such as bentonite, pozzolan, perlite, kaolin, ferromanganese, barite, zeolites, a little sulphur and most importantly, the unique type of clay which is known since the prehistoric times as the “Kimolian earth” that took its name after the island and due to its color and texture, gave it to “kritida”, our well-known blackboard chalk. The semi-precious quartz minerals such as amethyst, agate, chalcedony, jasper, opal etc. are common on the island and can be easily found at the beaches like colorful pebbles.