Sarlluin (Sindarin: Blue Stone) is the light-blue stone found exclusively in the Blue Mountains. There, it is present in a layer overground, covering regular stone, and in randomly generated deposits underground.
It is similar to Sarngaran, which is found in the Red Mountains. While Tolkien himself never mentioned a type of rock specific to the Blue Mountains, this blue stone has been included to explain their name.
Sarlluin must be mined with a pickaxe. It can be alloyed with iron ingots or iron ore in a Dwarven forge to forge Blue Dwarven Steel. Sarlluin can also be used to craft Sarlluin bricks, stairs, slabs, pillars, walls, pressure plates and buttons on a vanilla crafting table. a block of Sarlluin can be smelted into a Scorched Stone.