Granite is mostly quartz and plagioclase. The quartz is the hardest mineral with a hardness of 7. I would recommend a saw with diamond coated blades for the best mileage. A corundum coated blade would also work but would be less durable. Diamond and Corrundum have a hardness of 10 and 9 respectively but the mohs hardness scale in relative so diamond is orders of magnitude harder than any other mineral.