Abstract

Barite precipitation was induced by mixing sulfate and barium solutions to investigate conditions under which barite is most likely to be localized on microbial substrates, and hence most likely to preserve biogenic textures. Addition of sulfate solution to barium solution resulted in precipitation of intergrown platy, dendritic "angel wing," and microgranular barite in solution. Bacterial streamers and extracellular polymeric substances (EPS) collected from a cold sulfur spring acted as loci for precipitation of euhedral bowtie, intergrown platy, and intergrown tabular barite crystals, and scalloped platy barite crystals when sulfate solution was added to barium solutions in which they were immersed. Desiccation of bacterial streamers previously exposed to barium solution also produced subhedral platy and elongate anhedral barite crystals on extracellular surfaces and EPS. Immersion of barium-exposed streamers in sulfate solution produced scalloped platy barite crystals distributed through EPS and forming radial strings around bacterial filaments. Accidental exposure of streamers to iron produced amorphous iron oxides, as well as novel single and intergrown mixed-oxygenation-state barite/FeS "sandwiches." Distinct barite crystal habits and textures were observed in experiments conducted with and without bacterial streamers, suggesting that microbes have potential to influence the petrography of barite precipitated in sulfate-limited microbially colonized environments.