Is This Stone Ok In Tank ?

Hi

Just wanted to double check....

My LFS said it was fine for an aquarium - I asked three different people.

However on getting it home it seems really chalky, and when washing it the stone almost seems to disolve when rubbed - just like chalk.

I have seen this type of stone at a number of fish/pond shops so am wondering if it's ok for outdoor ponds but not aquariums.

Anyone recognise it ?

Thanks for advice !

Drop some vinegar on it it, if it effervesces then it wont be suitable unless you're keeping African Cichlids.

Done that - no fizz - so in it goes !

Thanks so much !