Amethyst

Amethyst is a members-only item on the OSRS Grand Exchange in the other category.

In-game examine text: "Maybe I can make something with this."

It has a Grand Exchange buy limit of 13,000 every four hours, a high alchemy value of 2.3k gp, and item ID 21347.

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Amethyst shows an active flip setup with a margin of +28 gp and 761,122 trades over the last 24 hours.

At the buy limit of 13,000 every four hours, max profit per cycle is about 364.0k gp — high margin with healthy liquidity.