Limestone

Limestone is a resource found in the world. It is used only to craft Concrete, an essential material in factory construction.

Obtaining
Limestone may be located using the Resource Scanner after completing the tier 0 milestone "Hub Upgrade 2". It can be mined by hand or by using any of the miners.

There are currently 75 Limestone Resource nodes in-game; 6 impure, 46 normal, and 23 pure. This means the upper limit of harvest rate is 57.000 Limestone/min (Mk3 miners, 250% overclock, Mk6 belt).