Well I personally 'collected' these rocks from rock pools areas at a beach I was holidaying at in December. They would have been weathered by the sea in those rock pools for hundreds, thousands or millions of years so I think they have cured pretty well. If mother nature put them there I am sure they will work in my tank.
Besides, they are 'base' rock. I am going to put lots of my current tank live rock all over them. They are only there to add structure.