Almost every state in the union has several quartz crystal mines. Arkansa is famous for its giant clear quartz crystal groupings on a limestone matrix. Missouri has pretty much the same stuff. Check out the "tri sate mining district rock and mineral locations" I dont know whether those are the exact google groupings of words but Im aware of several sites in the Joplin and tri-state districts.
Arkansa has a real honest to god kimberlite pipe or two, where diamonds can be found. (Diamonds are gonna be next year "beany babies" they are so overvalued now and the new CAnadian fields coming on line will make diamonds as common as "cubic zirconia"
One of the best quartz crystal sites in the US is the Rose quartz sites north of Ab NM ( I wont tell dys or hell be out there with a dozer), and other Rose quartz crystal sites are in Northern MAine, SOuthern Cal, and in North CArolina.
NEat doubly twinned quartz crystals (called Herkimer Diamonds) are found in Herkimer county NY.
We are a huge country knee deep in crystals. You wont make any money finding em. The best way to mine crystals is to buy a tract of land where some are found, and mine tourists with one of those "hunt and keep crystal mines". These are-to me, a tourist scam. Find a decent geology department at a major U and ask the mineralogy professors wheres some good sites. They are mostly rockhounds with PhD's anyway. All mineralogists I know are just big kids with fancy lab toys and a job that lets em go out in the field hunting for crystals.
HAve fun, .