The mineralogy, trace element concentrations in the solids, and leaching characteristics of spent shales from retort 3E cores were studied. This is the first comprehensive study of in situ generated materials. Although there were unique aspects to the operations of retort 3E that are not representative of a commercial operation, the study of in situ generated materials has provided insights into the chemical, mineralogic, and solution reactions that occur during and subsequent to underground retorting. Characterization of the solid materials has verified that in situ processing occurs in a thermodynamic and kinetic regime not previously encountered for surface retorting. Carbonate decomposition and silication reactions that form high-temperature products, such as akermanite-gehlenite and diopside-augite solid solutions, have been identified by x-ray diffraction. Observations resulting from solids characterization are substantiated by leachate chemistry, which, although compatible with leachates generated from surface retorted materials, are different in extent (composition and concentration). Comparison of leachates generated from in situ materials with Multi-Media Environmental Goals/Minimum Acute Toxicity Effluent values indicates that the major and trace elements deserving further investigation are potassium, lithium, fluoride, vanadium, boron, molybdenum, nickel, and arsenic. Several trace elements, including fluoride, vanadium, boron, and arsenic, show increased mobilities from spent shales containing akermanite-gehlenite solid solutions as the major mineral phase. This report details the chemical, mineralogic, and solution behavior of major, minor, and trace elements in these minerals.