In this video, a geologist describes how coal, a sedimentary rock, was formed when organic materials piled up in swamps millions of years ago. Over time, heat and pressure transformed the buried materials into peat and into various forms of coal. The geologist shows samples of low- and high-sulfur coal. High-sulfur coal contains a lot of pyrite, which is a mixture of sulfur, iron, and traces of other minerals. As long as it is underground, this mixture causes no environmental problems. But when it is exposed to air through mining, the pyrite rusts and forms sulfate salts on the coal’s surface that can contaminate water.
This video resource is part of KET’s Water Solutions collection at PBS LearningMedia.