Block of oil shale (marlstone) and a beaker of the crude oil (kerogen) that is derived from it. Oil shale is a fine-grained rock that contains varying amounts of kerogen, an organic material. Heating or retorting (distilling) to 900 degrees F. yields a synthetic oil and gas. This specimen is from the Green River formation, a major U.S. deposit spread over the Colorado-Wyoming-Utah area.