Can these rocks be used

[aquascapist]

Hi Guys,
Found these by dozens near mehraulli. can it be used for planted tanks? locals call it khangar. possibly a byproduct from iron blast furnaces i think. need advice. thanks!!

[SCORPIO]

Khangers also contain metals and not good for the health of fishes/invertebrates. So It is good to not use in aquarium. You can buy rocks from Meharuli Road to use in Aquarium.

[aquascapist]

Rajivji, thanks for the fast reply. Hmm ok will not risk using this. I thought it might be substituted for lava rocks. I was thinking of using it to raise the substrate depth for a hill look. Can you suggest me some ideas. Thanks

[discus sing]

these rocks contain furnace oil for casting purpose, so not to use these