Sandstone. Not recommended
Water-worn pebbles of varying sizes can give a very natural look to an aquarium. Sandstone is mostly safe to use for all tanks after the standard cleaning protocols; however it is a sedimentary rock made from small grains of quartz and feldspar.
Note; due to the feldspar, (which can contain potassium, sodium or calcium) it may be harmful.
guess i should of sed it wasnt reccomended then.