Oil shale industry is an industry of mining and processing of oil shale—a fine-grained sedimentary rock, containing significant amounts of kerogen (a solid mixture of organic chemical compounds), from which liquid hydrocarbons can be manufactured. The industry has developed in Brazil, China, Estonia and to some extent in Germany and Russia. Several other countries are currently conducting research on their oil shale reserves and production methods to improve efficiency and recovery. However, Australia has halted their pilot projects due to environmental concerns. Estonia accounted for about 70% of the world's oil shale production in a study published in 2005.