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