Não informado. (1931). Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences.
Citação do estilo Chicago (17ª ed.)Não informado. Mineral Industries. State College, Pa: Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
Citação MLA (8ª ed.)Não informado. Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
אזהרה: ציטוטים אלה לעיתים לא מדויקים ב 100%.