When passing by the island of Fur, notice the cliffs near the shoreline with their many distinct geological layers. The island is known for its deposits of diatomite, a mineral that forms from algae and was first used by the Greeks over 2,000 years ago in pottery. Pure deposits of the golden-brown material are both rare and valuable, as the mineral's honeycomb structure gives it remarkable filtering and absorbent qualities. (It is used in everything from swimming-pool filters to soil amendments.) You can spot it along the shoreline in Fur's prominent cliffs, with their beautiful tiers of varying hues reflecting the layers of sediment in these geological formations.