Crushed limestone is one of the items used to make pig iron.
Crushed limestone is creamish white in color, similar in shade to limestone. It appears similarly to pigments, being a powder.
Crushed limestone must be crafted on a press.
Crushed limestone can be used to craft plaster at a builder's bench.
Crushed limestone can be used to craft pig iron, which then can be used to make iron ingots with less iron ore.
In the real world, limestone contains calcium carbonate, which is used in the purification of iron from ore by reacting with sulfur, an impurity within iron ore.