by Abdurrahman Murat:
Oil shale is commonly defined as a fine-grained sedimentary rock containing organic matter (kerogen) that yields substantial amounts of oil and combustible gas upon destructive distillation (retorting). Most of the organic matter is insoluble in ordinary organic solvents; therefore, it is decomposed by heating to release such materials. What derives the importance of oil shale to produce energy including combustible gas and a number of procured products is how economic it can be recovered.
Deposits of oil shale having economic potential are generally those that are at or near enough to the surface to be developed by open-pit, conventional underground mining or by in-situ methods. Oil shales have a wide range of organic content and oil yield. Commercial grades of oil shale, as determined by their shale oil yield, ranges from about 100 to 200 liters per metric ton (l/t) of rock. The U.S. Geological Survey has used a lower limit of about 42 lt/ton for classification of federal oil-shale lands.