Which object can scratch feldspar but not quartz?
A modern watch works using something called a crystal. The crystal is a little chunk of a mineral that vibrates when you apply a small amount of electricity to it. This is called the 'piezoelectric principle'. The vibration is very consistant, so if you electronically count the vibrations you can use them to measure time. A quartz watch uses a quartz crystal. By the standard of wind-up watches with mainsprings, a quartz watch is just incredibly accurate. But the technology is very cheap these days because they make so many of them.
I think that is they type of battery or something from prevents it from being needed to be wound (I stopped wearing watches long ago)