Petrified Chemical Gardens

Abstract

Chemical gardens are tubular structures that consist of inorganic precipitate membranes formed under far-from-equilibrium conditions. Their possible existence in natural geological settings complicates the differentiation between Earth’s earliest microfossils and abiotic structures as well as the search for life signatures on other planets. Here, we address the question whether laboratory-grown chemical gardens can withstand encapsulation in a slowly forming inorganic matrix. We report high-temperature conditions for which FeCl3-derived chemical gardens persist for several months allowing the surrounding silicate solution to solidify. This crystallization typically starts on the surface of the chemical gardens, slowly embeds them within spheroidal globules, and finally spreads across the entire system to create a rock-like sample with the preserved chemical garden as a complex inclusion. We show that the initially solution-filled interior of the tube also undergoes solidification with minor amounts of iron present. The main matrix material is identified as polycrystalline sodium silicate hexahydrate. The results can be compared to enigmatic mineral tubules preserved in some natural geological settings (e.g., agates), which in some instances show spheroidal overgrowths of quartz.