granite thickness is about 18-20mm.. where else quartz comes in 12mm, 15mm, 20mm.. so it all depends.

In terms of heaviness.. both are bloody heavy lol. But a lot of sifus have mentioned before that granites are usually tougher and quartz slightly more brittle (during handling and transportation where they have to carry and move the stones around) .. although in my experience on the surface itself during completed works, quartz are more durable. Try using a key and scrub on quartz, it shouldnt scratch, any scratch mark is from the key and can be cleaned off.. where else do that on the granite.. you may get a permanent scratch mark.