you can use a small crystal as a seed crystal. In the case of quartz you will need temperatures and pressures not normally available outside a lab. It's cheaper to find or buy a larger natural crystal or buy a lab grown one, which are pretty interesting.
Quartz crystals form deep in the earth where there's a lot of heat and pressure. The quartz crystals are able to grow because the heat in the earth slowly diminishes as the rocks are pushed to the surface due to tectonic movement or volcanoes, giving time for the minerals to slowly cool and form into large structures. Look at igneous rocks, the extrusive rocks don't normally have crystals because they cooled too fast, intrusive rocks have large crystals because they cooled slowly.
