Limestone brick

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

In-game examine text: "A well carved limestone brick."

It has a Grand Exchange buy limit of 10,000 every four hours, a high alchemy value of 12 gp, and item ID 3420.

View on OSRS Wiki

Limestone Brick shows an active flip setup with a margin of +56 gp and 15,125 trades over the last 24 hours.

At the buy limit of 10,000 every four hours, max profit per cycle is about 560.0k gp — high margin with healthy liquidity.