TY  - RPRT
TI  - PROTON MICROPROBE ANALYSIS OF TRACE-ELEMENT VARIATIONS IN VITRINITES IN THE SAME AND DIFFERENT COAL BEDS.
AU  - J.A. Minkin
AU  - E. C. T. Chao
AU  - Herma Blank
AU  - F.T. Dulong
PY  - 1987
UR  - https://pubs.usgs.gov/publication/70015225
ID  - 70015225
ER  -