Erionite series minerals in felsic volcanic rocks of southern Mesa Central, Guanajuato, Mexico

Trace quantities of erionite series minerals were identified along with chabazite, clinoptilolite, and morderite within Chichindaro rhyolites (~ 30 Ma) at latitude 21°8′30″–21°17′00″ and longitude 101°5′00″–101°10′00″, ~ 15 km south of the present-day town of San Felipe in the state of Guanajuato, Mexico. Special attention was given to the erionite -K, Na, and Ca varieties. Despite their occurrence in trace amounts, image analyses of these minerals with the aid of Scanning Electron Microscope indicates the existence of both hair-like and needle-like fibers that are 5.85–29.26 μm long and 2.510–0.252 μm thick, which allows them to be categorized as “inhalable” (with length > 5 μm and thickness