Não informado. (1931). Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences.
Citace podle Chicago (17th ed.)Não informado. Mineral Industries. State College, Pa: Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
Citace podle MLA (8th ed.)Não informado. Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
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