In May of 1981, a retorted oil-shale waste pile and an oil-shale mine were sampled at Rulison, Colorado. The oil shale mine and retort was operated by the US Bureau of Mines from 1926 until 1929. In the Colorado-Utah-Wyoming region, the Rulison site contains the only sizeable area of retorted oil-shale waste representing retorting activities before 1950. The oil shale was mined above the plant and retorted by processes similar to those used for modern above ground retorting. The objectives of this study were to investigate the chemical and mineralogical changes during 50 years of weathering of spent shale and differences between the chemical and mineral composition of the oil shale used in the retorts and the retorted oil shale waste.