Hi
Don't see why not if sifted to remove dust. You might place some in a bowl of vinegar to check for chemical reaction. If the material will disolve in water the vinegar will bubble. Means that there is soluable material and will play havoc with your pH long term. gary

Speaking as a geologist - if it is truly granite, you are fine; granite is composed of silicate minerals that are essentially incapable of being affected by fresh water.

The vinegar test is not foolproof. Dolostone is a very common rock, most people would think it was limestone and in appearance it is very similar ro limestone - but it s made up mostly or entirely of the mineral calcium magnesium carbonate. It will not fizz in cold vinegar but will diissolve in water - not as easily as limestone but easily enough to affect the water chemistry. There are other rocks that do not fizz but are unsafe. For nstance, avoid anything with sulfides, which includes pyrite (fools gold). Anything in the granite family, including diorite and gabbro, is OK. Most slate, but not all, is fine, and gneiss is all right.

Granite is basically quartz,hornblend,and feldspar it is safe to use.I use it in my 40 gallons aquarium.

Granite is safe to use I use it in my aquarium as gravel.