2016 Volume 122 Issue 2 Pages 45-60
A well-known terrace-forming hot spring is located at Saturnia in the Maremma area of southern Toscana, Italy. The waters are circumneutral (pH around 7), mesophilic (around 37°C), and give off a strong sulfurous odor. Pisoliths, brown limestone, and green microbial mats are found in the area. Hot spring structures and compositions are determined based on mineralogical and chemical data obtained with a powder X-ray diffractometer (XRD) and an X-ray fluorescence analyzer (XRF). Microbial parameters are determined on sub-millimeter scales using a scanning electron microscope, equipped with an energy-dispersive X-ray spectrometer (SEM-EDS).
XRD results indicate that the pisoliths are composed of calcite, native sulfur, and quartz, whereas the brown limestone contains mica, native sulfur, chabazite, and 7 Å clay minerals. XRF analysis indicates that the pisoliths contain mainly C, O, Ca, S, Si, and Sr, whereas the brown limestone contains high concentrations of O, S, Al, K, Ca, Fe, and Na. Because the pisoliths are Ca-rich, concentrations of heavy metals (Sr, Sn, and Pb) at the aqueous interface can be explained by combining XRF chemistry, XRD mineralogy, and SEM-EDS observations of green microbial mats. SEM-EDS elemental maps of the pisolith indicate the presence of apatite and framboidal pyrite crystals.
