TY  - RPRT
TI  - Recommended procedures and methodology of coal description
AU  - E.C. Chao
AU  - J.A. Minkin
AU  - C.L. Thompson
PY  - 1983
DO  - 10.3133/cir894
UR  - https://pubs.usgs.gov/publication/cir894
ID  - cir894
ER  -