Não informado. (1931). Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences.
Chicago-Zitierstil (17. Ausg.)Não informado. Mineral Industries. State College, Pa: Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
MLA-Zitierstil (8. Ausg.)Não informado. Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
Achtung: Diese Zitate sind unter Umständen nicht zu 100% korrekt.