The coprecipitation of barium carbonate and silica spontaneously creates complex micrometer-scale objects such as sheets and helices. These structures consist of densely packed crystalline nanorods that in the case of sheets align in radial direction. We report the existence of an additional level of self-organization that creates oscillatory height variations in biomorph sheets. These topographic features take the form of either concentric rings or disordered, patchy patterns and form immediately in the wake of the crystallization front. Their wavelength varies around 6.5 μm and shows no pronounced dependence on the reactant concentrations. Atomic force microscopy reveals height variations of up to 500 nm which equal 45% of the average sheet thickness. These undulations are accompanied by a systematic out-of-plane displacement of the nanorods. Our results are discussed in the context of an earlier hypothesis that predicts pH oscillations near the crystallization front.

Biomorphs are life-like microstructures of selfassembled barium carbonate nanorods and silica. In a departure from established approaches, we produce biomorphs in CO2- and gradient-free solutions. Our study reveals novel structural motifs for solution-grown biomorphs, reduces pH transients, and expands the upper pH limit for biomorph formation to over 12 where silica is essentially soluble.

A fundamental problem in chemistry is the nontrivial extension of molecular complexity to macroscopic length scales. The exploration of such concepts offers profound insights into the hierarchical organization of living matter and promises a novel engineering paradigm under which materials and devices are grown biomimetically far from the thermodynamic equilibrium. Inorganic microstructures called biomorphs are an ideal model system to develop such approaches. They are polycrystalline nanorod assemblies that form in basic solution from alkaline‐earth metal ions, silicate, and carbonate. Biomorphs range in size from tens of micrometers to millimeters and form over several hours under simple experimental settings. Their noneuhedral, life‐like shapes include surprising leafs, helices, funnels, urns, and coral‐shaped motifs. Here we review the current understanding of biomorphs, highlight links to nonlinear chemical dynamics, and discuss applications in materials science and astrobiology.