Opal

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

In-game examine text: "A semi precious stone."

It has a Grand Exchange buy limit of 13,000 every four hours, a high alchemy value of 60 gp, and item ID 1609.

View on OSRS Wiki

Opal shows an active flip setup with a margin of +13 gp and 75,779 trades over the last 24 hours.

At the buy limit of 13,000 every four hours, max profit per cycle is about 169.0k gp — high margin with healthy liquidity.