id	keyword
gc-880	coal
gc-880	seam
gc-880	coal seam
gc-880	content
gc-880	iii
gc-880	lignite
gc-880	et al
gc-880	elements
gc-880	kovin
gc-880	seam ii
gc-880	table
gc-880	ash
gc-880	trace
gc-880	doi
gc-880	minerals
gc-880	samples
gc-880	field
gc-880	coal geology
gc-880	fig
gc-880	serbia
gc-880	journal
gc-880	kovin lignite