Granite is mostly silica (SiO2 ~70%), and Al2O3 (~10%) and numerous oxides in lesser percentage (potassium, sodium, iron, magnesium, titanium, etc.). It is pretty much inert in saltwater, but the K, Fe, Mg, (not a big issue) as well as other ions (who know what) may leach out over time... not a good idea unless you feel that the advantage out weight the potential problem.
the reason i ask is that i construction company was just going to give me some...i wasn't sure if it would work. i will continue looking. any ideas of places i may find some rock that's worth curing?
Granite is very dense and comes in pretty boring shapes. I guess this is ok just as a foundation for a reef structure but it wouldnt be too interesting. Also the main benefit of live rock is the anoxic bacteria living deep inside the pores of the rock. I doubt granite even has any deep pores, it's pretty solid and dense. Limestone is a mush better way to go, as it is naturally formed in the bottom of the ocean, and is what most live rock is anyway...
Ditto meloco14's comment. With granite and boring, that reminds me of the ability of some reef critters to dig/bore thru rocks and make tunnels. With granite, because it is so chemically stable that nothing can cut thru it. Another beneift of limestone is that it can provide some degree of buffering, albeit small, but you can't get any from granite.
