Mordenite is an aluminosilicate zeolite mineral similar to asbestos. The unique structural and chemical properties make mordenite favorable to a wide variety of commercial applications ranging from waste-effluent treatment to paper production. Interest in mordenite, as an occupational inhalation hazard, arose when it was discovered that the fibrous form of the mineral exists in the subsurface of Yucca Mountain, NY, the site of a federally proposed nuclear waste repository. During preliminary geologic investigations at Yucca Mountain, workers performing dry-drilling operations were potentially being exposed to aerosols of mordenite. In addition, environmental exposures to zeolites (including mordenite) were brought to the world's attention when a reported outbreak of mesothelioma was documented in the Cappadocia region of Turkey. While the precise mechanism for the production of an adverse biological response is yet unknown, increased scrutiny is being placed on a fiber's dimensional characteristics and biopersistence (durability) and the role they play in the induction of pulmonary disease. Although the morphology of aerosolized mordenite has been reported by at least one researcher, what has yet to be investigated is the biopersistence of mordenite fibers upon deposition in the pulmonary environment. Research studies have shown that a fiber's in-vivo biopersistence is related to the degree of its in-vitro dissolution. Methods for measuring in-vitro fiber dissolution for durable fibers have been developed using acidic solvents, representing the environment within alveolar macrophages (pH of 4.5-5.0). This research acquired and aerosolized mordenite minerals deposited in different regions of the United States. Each mordenite mineral was analyzed for it major mineral and chemical constituents. Fiber samples from each specimen were collected and evaluated for their respective morphologic characteristics and subjected to an acidic simulated lung fluid assay in an effort to gain a better understanding of their pulmonary biopersistence. Results of the aerosolization phase of this research suggest that mechanical aerosolization of fibrous mordenite minerals can cause an environmental release of fibers having small diameters (< 1 micromm) and large aspect ratios. Performance of the dissolution phase of this study identified an optical method to evaluate fiber dissolution and suggests that mordenite fibers are insoluble at acidic pH. It is anticipated that duplication of methods performed in this study will facilitate the estimation of fiber biopersistence at both intra-cellular and extra-cellular pH. In addition, the study results will also provide epidemiologists conducting health hazard studies on fibers a mechanistic basis for the bioavailabilty of mordenite fibers in the lung.