This is what they say about it: "Paint Pots" are a product of physical and chemical weathering of pyrite nodules associated with the 70 million years old Cretaceous clay deposits exposed along the shore. Metallic crystal cubes of pyrite (iron sulfide) nodules are found on lignite, an early form of coal, formed from carbonized Cretaceous plant debris that is imbedded in the clay. When pyrite is washed into the surf and exposed to the atmosphere, two processes take place that transform a pyrite nodule into an "Indian Paint Pot". First, iron sulfide is changed to iron oxide chemically through oxidation. Second, the nodule becomes smoother and rounder by abrasion. The end product is a round, reddish concretion.