COMPARISON OF ERIONITE FROM N. DAKOTA AND CENTRAL TURKEY
Three aspects of erionite are considered: morphology, crystal structure, and composition. SEM images of in situ erionite show very similar morphology. ND and T are fibrous with lengths up to 50 microns and length to width ratios of about 10, but with an extended range. Each fiber typically shows individual fibrils with spalling at fiber ends suggesting easy breakup to thinner and shorter fibers. Release of these fibers from the friable host rock by mechanical abrasion would most certainly involve creation of shorter fibers into a size range which would allow inhalation.
While erionite is assumed, the known framework structure of erionite was confirmed by obtaining single crystal intensity data at the CARS beamline at the Advanced Photon Source. For both ND and T, the cancrinite cage was nearly fully occupied by K; the erionite cage showed a complex distribution of Mg, Ca and Na mainly along the 6-fold axis but masked by positional disorder. Special attention was given to recognition of diffractions which would indicate an intergrowth of erionite and offretite, but for both ND and T, no offretite is present at an detection limit of 5%.
Analyses were done by SEM-EDS for in-situ grains and by EMP-WDS for grains mounted on flat conductive tape. Bulk analyses are suspect due to impure samples; the balance error test does not indicate purity as other zeolites and feldspars also meet this criteria. Both T and ND erionite showed expected Si, Al, K, Ca, Na, Mg: Fe is below 0.30 wt%, while Sr and Ba are below detection (~200 ppmw). The Si/(Si+Al) atom ratio is 0.78 for ND and 0.80 for T (both +/- 0.01). T erionite has distinctly more Na and K than ND erionite, while MgO is 1.5 – 2% in both.
In summary, there is no compelling reason to consider that these two erionite samples differ. While some compositional differences are apparent, there is no a priori reason to expect that these differences will affect their carcinogenicity.