X-ray diffraction intensity ratios I(111)/I((3)over-bar11) of natural heulandites and clinoptilolites

Heulandite-group zeolites are abundant in the Miocene pyroclastics from Wes tern Anatolia, Turkey. We investigated the relation between the I(111)/I((3 ) over bar 11) intensity ratios measured by X-ray diffraction (XRD) and the content of exchangeable cations for 15 samples of natural heulandite-group minerals gathered from the Gordes and Bigadic regions of Western Anatolia. The intensity ratios range from 0.77 to 0.94 in natural heulandites and fr om 1.38 to 1.80 in natural clinoptilolites. The data obtained from Na-, K- and Ca-exchanged forms of a heulandite and clinoptilolite show that the int ensity ratio increases with Na-, K- and Ca-exchange in heulandite and also with Na- and K-exchange in clinoptilolite, whereas it decreases with Ca-exc hange in clinoptilolite. The intensity ratios were calculated using the kno wn structural data of clinoptilolites to understand the effect of positions , amounts and kinds of exchangeable cations and water molecules. An increas e in Na and Ca may increase or decrease the intensity ratio, depending on t heir sites and occupancies. Potassium causes a significant increase in the intensity ratio and an increase in Mg decreases the intensity ratio. There is a strong correlation between the intensity ratio I(111)/I((3) over bar 1 1) and (Na + K)/(Ca + Mg) ratio and thermal stability, both of which have b een used to characterize heulandite-group minerals.