yep, shell turns to lime in an oxidized atmosphere.... it will pit. so also will any gypsum crystals (fired ,they turn to plaster)
all earthenware pots are porous. Burnishing the interior with a stone helps, but they're still porous. water will seep through.
BUT, if you grease the interior of a burnished pot, you'll have MUCH better holding and much less seeping through.
when you cook with an earthen pot you must keep the pot from boiling dry..if the liquid is gone the fire WILL likely crack the pot.