charcoal, coal
炭 centers on black, carbon-rich material used for burning: charcoal and coal. Both are solid fuels produced from organic matter.
炭 combines 山 (mountain) and 灰 (ash), suggesting material from mountains that becomes ash when burned. This fits the idea of charcoal or coal.
Picture a mountain 山 of ash 灰: the ash comes from burning charcoal or coal, so 炭 means charcoal or coal.
For タン, imagine a tan-colored piece of charcoal: tan -> タン, and the charcoal is that dark tan color.
carbonic acid
carbohydrate
carbon (C)
charcoal
coal
carbon dioxide; CO2
coal mine; (coal) pit; colliery
charcoal fire
carbonization; carbonisation
charcoal
anthrax
briquette (charcoal or coal)
charcoal making; charcoal maker
activated carbon; activated charcoal
peat
charcoal dealer
partly burned charcoal
carbonated spring; soda spring
sawtooth oak charcoal
rice husk ash (used for soil conditioning)