Charcoal

Charcoal is a free-to-play item on the OSRS Grand Exchange in the ores category.

In-game examine text: "A lump of charcoal."

It has a Grand Exchange buy limit of 13,000 every four hours, a high alchemy value of 27 gp, and item ID 973.

View on OSRS Wiki

Charcoal shows an active flip setup with a margin of +11 gp and 6,287 trades over the last 24 hours.

At the buy limit of 13,000 every four hours, max profit per cycle is about 143.0k gp — high margin with healthy liquidity.