background
black
black background
black gold
board
bucket
carbon
carbon dioxide
chp
coal
coal pile
coal structure
combustible
dark
deposits
energy
energy source
energy storage
exploitation
extraction
fossil
fossil fuel
fuel
hammer
hand tool
hard
industrial
industry
lump
metal bucket
metal clamp
mine
mineral
mining
night
pick
pollution
potential
production
raw material
rock
shale
solid fuel
stone
to be burned
tool
unclean
underground
wealth
wooden box