Coal

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

In-game examine text: "Hmm a non-renewable energy source!"

It has a Grand Exchange buy limit of 13,000 every four hours, a high alchemy value of 27 gp, and item ID 453.

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Coal currently has a flip margin of −2 gp, which isn't profitable to flip right now despite 23,960,669 trades over the last 24 hours.

Items with negative or zero margins like this are better watched than actively flipped until the spread widens.