Oil shale in Estonia
There are two kinds of oil shale in Estonia, both of which are sedimentary rocks laid down during the Ordovician geologic period. Graptolitic argillite is the larger oil shale resource, but, because its organic matter content is relatively low, it is not used industrially. The other is kukersite, which has been mined for more than a hundred years. Kukersite deposits in Estonia account for 1% of global oil shale deposits. Oil shale () has been defined as a strategic energy resource in Estonia and the oil shale industry in Estonia is one of the most developed in the world. Historically, most of mined oil shale was used for electricity generation. Of all the oil shale fired power stations in the world, the two largest are in Estonia. Although its share decreased in the decade to 2022, direct and indirect use of oil shale still generates about half of Estonia's electricity. About half of mined oil shale is used to produce shale oil, a type of synthetic oil extracted from oil shale by pyrolysis, which is sufficient to keep Estonia as the second largest shale oil producer in the world after China. In addition, oil shale and its products are used