While shopping at the poultry feed dealer, I bought 50 lbs of pullet size oyster shell for $10.
The oyster shell is white and is mixed with ABBA mineral.
I marvel at how hens have the ability to adjust their intake of calcium according to their individual needs. When mineral is fed free choice, the hens will dramatically increase their mineral consumption when their chicks are about ten days old and continue eating a small dish a day until the subsequent clutch is laid.
If the hen is raising the chicks by herself, when she starts eating more mineral, it is time to re-introduce the male again!