The rocks are speckled with obsidian, black on ocre. In no other place of the Meditterranean does the lavic water present itself in this blot formation .

The pure obsidian glass, is in its natural form, brilliant black. Primitive man used to make spears, axes, knives from it. The Obsidian which is extracted from the island of Palmarola was worked in Ponza and in Zanone, where remains have been found it is likely that finished products were then trasported to the Circeo.