carbon
碳 centers on the chemical element carbon, often associated with charcoal or coal-like substances.
碳 is a modern character created for the chemical element carbon. It combines 石 (stone) with 炭 (charcoal), reflecting carbon's association with coal and minerals.
Stone 石 and charcoal 炭 together represent carbon: the element found in both rocks and burnt wood.
For タン, imagine a ton of carbon: ton -> タン, and the stone-like charcoal piles up.
—