Raw oil shale samples were investigated to provide baseline information on sulfur-bearing mineral composition. The sulfur-bearing mineral identified in raw oil in this study was primarily pyrite (FeS{sub 2}). Sulfur-bearing alteration minerals were gypsum (CaSO{sub 4}{center dot}2H{sub 2}O) and copiapite (Fe{sub 14}O{sub 3}(SO{sub 4}){sub 18}{center dot}63H{sub 2}O), which appeared as crystalline masses on the surfaces of sulfide minerals. Investigation of spent (or processed) oil shale demonstrated that heat-induced mineralogical reactions can drastically alter the crystalline structure of materials. Hexagonal pyrrhotite is the kinetically and structurally preferred sulfur-bearing mineral formed during oil shale processing. The Ca-monosulfide oldhamite was identified in processed Green River Formation oil shale resulting from WRI's TREE process. Oldhamite which has not been identified in terrestrial rocks, formed as a result of high sulfur gases present during the thermal processing of a Ca-rich oil shale. This work provided information concerning (1) thermal alteration of pyrite to pyrrhotite (and pyrrhotite-type minerals) and (2) the disclosure of a mineral not previously reported in oil shale. It is essential for processing and disposal considerations that metastable and unstable mineral forms be identified and more completely understood. Information concerning processing characteristics and sulfur-bearing mineral forms in raw and processed oil shale can be incorporated into the future strategies of solid waste management for fossil fuels. 56 refs., 21 figs., 3 tabs.