If you had one ton of bituminous coal with an energy content of 25 million BTUs, the energy released upon combustion would still be approximately 25 million BTUs, regardless of how long it had been laying there, assuming it had been stored properly and retained its energy content. Coal is classified into several types based on its carbon content, energy content, and degree of metamorphism.  1. Anthracite Coal - Carbon Content: 86-97% - Energy Value: Approximately 25-35 million BTUs per ton. - Characteristics:    - Highest rank of coal, hard and lustrous.   - Burns cleanly with a high heat output and low smoke. - Uses: Primarily used for residential and commercial space heating and in industrial processes where high energy content is required. 2. Bituminous Coal - Carbon Content: 45-86% - Energy Value: Approximately 24-35 million BTUs per ton. - Characteristics:    - Soft and typically black, with a shiny appearance.   - Contains volatile co...