STRUCTURE AND GROWTH-MECHANISM OF MINERAL DENDRITES

THE surfaces of limestones are often marked by black or red-brown deposits known as mineral dendrites 1,2. These are deposits of hydrous iron or manganese oxides formed when supersaturated solutions of iron or manganese penetrate the limestone and are precipitated on exposure to air at the surface. Mineral dendrites have a fractal 3 appearance, but the origin and characteristics of this morphology, and its dependence on concentration gradients or reaction rates have been little studied. Here we analyse the shapes and fractal properties of mineral dendrites from several different origins, and propose a lattice reaction-diffusion model for their formation. The model shows how different reaction conditions can account for the variation in fractal dimension observed in real dendrites.