CRYSTALLOCHEMICAL VARIATION AND GENESIS OF MORDENITE, MARYSVALE, UTAH

Approximately 6.5 km west of Marysvale, Utah, in Beaver Creek Canyon, is an outcrop of mordenite and volcanic glass. In a roadcut, the outcrop consists of both pink and green form of mordenite, brown glass, and quartz-feldspar spherulites. The pink mordenite seems to be associated with the brown glass. The green mordenite is massive and is not in contact with the brown glass, but is always separated from it by the pink mordenite. Green volcanic glass is found cropping out up the slope in association with the green mordenite. Variations in exchangeable cation (Na, Ca, and K) and trace element (Rb, Sr, and Y) concentrations result from known crystallochemical preferences. Principle components analyses of electron microprobe data reveal an inverse relationship between Si and Ca+Na+Al, as well as an inverse relationship between Ca and Na. Pink mordenite hand samples containing remnants of the brown glass were extracted from Beaver Creek outcrop. Fe2+/Fe3+ ratios for green mordenite and green glass are similar and ratios for pink mordenite and brown glass are the same. The field relations and the Fe2+/Fe3+ ratios indicate a genetic relationship between the green glass and green mordenite and the brown glass and pink mordenite. K in the glass exchanged with Ca and Na in the fluid, thus enriching the mordenite in Ca and Na. Rb concentration is higher in the glass due to the relatively high concentration of K. Sr concentration is higher in the mordenites due to substitution for Ca and Na. Stable isotope data for structural oxygen reveal that the mordenites inherited most of their oxygen from the glass rather than the fluid involved in the alteration process.