We observed spontaneous formation of very complex structures, measurable on the centimeter and millimeter scales, in a simple dual-component inorganic chemical system. The diffusion, convection, and chemical reactions self-organize in space and time and produce domes, multi-arms, or more complex structures with different spatial organization depending on the concentration of reagents in the aqueous environment into which the 'seed' is immersed. (C) 2003 Elsevier Science B.V. All rights reserved.