Não informado. (1931). Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences.
Lua i Stíl Chicago (17ú heag.)Não informado. Mineral Industries. State College, Pa: Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
Lua MLA (8ú heag.)Não informado. Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
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