Não informado. (1931). Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences.
Chicagoスタイル(17版)引用形式Não informado. Mineral Industries. State College, Pa: Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
MLA(8版)引用形式Não informado. Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
警告: この引用は必ずしも正確ではありません.