If you are using natural gas then you will have some type of fire element. Simply build the fire pit so there is room enough between the fire and the edge of your granite top. That being said, we normally use limestone, bluestone or concrete for the tops of fire pits.

Ask the granite supplier what the heat tolerance is of the granite you are planning to use. He or she will be better informed on their own product and help to guide you in the correct direction.

Both of the fire pits below have concrete tops and are natural gas.

What's the reason for granite? I'd think about some of the options K&D mentions just to get a beefier top. 1.25" is ok, but 2" looks way better.

We have installed granite with gas burning and not had issues. Do not install one solid piece, minimum 2 pieces, 4 preferred with mortar/high heat caulk for expansion when the firepit heats up. Also minimize or eliminate the overhang on the inside of the firepit, 1"-2" is fine for the outside but flush on the inside helps the cap from trapping heat and getting too hot.

Like RG said, 2-3" thick looks better with any material.

About 8 years my mason built a firepit on our project and used limestone to cap it. The pool patio and the pool coping too was limestone to be consistent.

The inside was lined with fire brick. The homeowner however, built and inferno and the limestone cracked. So, just be careful on the size of the fire.

It may defy logic but have had the same scenario with limestone cracking if the homeowner builds a bonfire.

@Mystic....lolol