Arang batu: Perbezaan antara semakan
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* {{cite book |last= Smith |first= Duane A. |title= Mining America: The Industry and the Environment, 1800–1980 |year= 1993 |month= May |publisher= University Press of Kansas |location= Lawrence, KS |isbn= 0-87081-306-4 |page= 210}}
* {{cite book |last = Freese |first = Barbara|title = Coal: A Human History|year = 2003|publisher=Penguin Books|isbn = 0-7382-0400-5 |oclc = 51449422}}
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