Need help in breaking big rocks

[crazyhanz]

Has anyone here successfully broken up those grey looking rocks for iwagumi setups (normal ones bought from colorful, biotope, NA)? I have a couple of them at my disposal but am having a hard time breaking them. I tried using a hammer and all I get are just broken chips. Is there a method of breaking them to get bigger chunks? Please share with us on how you go about doing it. Thanks for sharing!

[vratenza]

you will need a masonry grade chisel and hammer...
Just using the hammer alone will just get the result you gotten.
Alternatively can try impact drill if you already have them.

*Most important!!! Wear proper eye protection goggles!"

[crazyhanz]

I see... Thanks for the input..
Any other ways people?

[Cacatuoides]

Get a electric drill and put it on hammer mode