Black tourmaline core

Black Tourmaline Core is a members-only item on the OSRS Grand Exchange in the ores category.

In-game examine text: "The blackened heart of the Grotesque Guardians."

It has a Grand Exchange buy limit of 5 every four hours, a high alchemy value of 24.9k gp, and item ID 21730.

View on OSRS Wiki

Black Tourmaline Core currently has a flip margin of −20.3k gp, which isn't profitable to flip right now despite 455 trades over the last 24 hours.

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