More than 100 minerals have been reported from the Silver Coin Mine, Nevada USA; five new minerals have been discovered here, due to the unusual geochemical environment. The present study reports on the investigation of a greenish clayey sample from the Silver Coin Mine. After the separation of a fine fraction to enrich the clay minerals, sauconite, a rare Zn-rich smectite, was found by X-ray diffraction (XRD) and was further characterized by differential thermal analysis (DTA), infrared (IR) spectroscopy and scanning electron microscopy (SEM). The Zn-rich smectite is accompanied by illite, minor kaolinite/halloysite and traces of gibbsite (as was indicated by the IR spectroscopy). The occurrence indicates an acidic environment probably caused by oxidation of sulfides.
The determination of the structural formula, to further characterize the Zn-rich smectite, was difficult because of the multi-clay mineral assembly. However, different SEM-EDX (energy dispersive X-ray) approaches as well as transmission electron microscopy (TEM)-EDX analysis helped to characterize the smectite as Al-rich sauconite with some exchangeable K+.