Gaya APA

Gruyter, P, D. (1941). A Preliminary Classification of Indian Coals to the Purpose of Their Technical Use . Bandung: Direktorat Sumber Daya Mineral.

Gaya MLA

Gruyter, P., DE. "A Preliminary Classification of Indian Coals to the Purpose of Their Technical Use". Bandung: Direktorat Sumber Daya Mineral, 1941. Batubara.