Crystal key

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

In-game examine text: "A mysterious key for a mysterious chest."

It has a Grand Exchange buy limit of 11,000 every four hours, a high alchemy value of 90 gp, and item ID 989.

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Crystal Key shows an active flip setup with a margin of +59 gp and 16,442 trades over the last 24 hours.

At the buy limit of 11,000 every four hours, max profit per cycle is about 649.0k gp — high margin with healthy liquidity.