What is the real difference between quartz and granite countertops?

Granite is cut from a block of natural stone. Quartz is about ninety percent ground quartz mineral bound with resin and pigment, pressed into a slab. That single difference drives everything else: granite is porous and needs sealing, quartz is not and does not. Granite tolerates a hot pan, quartz can scorch or discolour above roughly 150 degrees Celsius because of the resin. Granite varies slab to slab, quartz is repeatable. On price the two overlap heavily; the slab you choose matters far more than the material.