Herkimer Diamond Mine, Middleville, New York - http://www.herkimerdiamond.com/ Herkimer Diamonds is quartz faceted right in the ground!  I visited the Herkimer Mine in May of this year and was very impressed with the Scialdo family operation.  It's also a KOA Campground right on the Mohawk River and you can rent a pick ax and bucket to experience mining for yourself.  There is a gemstone museum and restaurant.  My personal favorite is the gift shop, which features all sorts of loose Herkimer Diamonds, mined right there on the property, as well as a fine collection of gemstones gathered from all corners of the world.  I recommend a visit if you're ever in the area. 

The Dayton Visual Arts Center, Dayton, Ohio - http://www.daytonvisualarts.org/