Gaya APA
Nyrola, J., lukkonen, M. (1987).
Ministry Mines And Enegy Of Indonesia Directorate Of Coal .
Bandung:
Pusat Sumber Daya Geologi.
Gaya MLA
Nyrola, Jukka., lukkonen, Matti.
"Ministry Mines And Enegy Of Indonesia Directorate Of Coal".
Bandung:
Pusat Sumber Daya Geologi,
1987.
Batubara.