Basalt

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

In-game examine text: "The crushed rock looks like it may react to other materials."

It has a Grand Exchange buy limit of 10,000 every four hours, a high alchemy value of 18 gp, and item ID 22603.

View on OSRS Wiki

Basalt shows an active flip setup with a margin of +7 gp and 270,218 trades over the last 24 hours.

At the buy limit of 10,000 every four hours, max profit per cycle is about 70.0k gp — high margin with healthy liquidity.