The process of extracting minerals, metals and other geological resources from the ground. Some materials that are mined are limestone, oil shale, diamonds, uranium, coal and iron. Generally, any practice that involves extraction of a non-renewable resource is considered mining. The nature of mining processes creates a potential negative impact on the environment during mining operations and even years after the mine is closed. As an industry, mining has contributed to global warming, acid mine drainage, and soil and air pollution resulting from toxic emissions from heavy metals.