As soon as I heard about Glitter Mountain, I knew it had to be a stop on our way to Tucson - even though technically it meant going north into a whole other state which wasn't in any way "enroute". Glitter Mountain is a Selenite mine that is commercially mined for a few months of the year, but is on public land so access is permitted. As we approached it, the entire side of the hill was glistening and sparkling white, looking almost wet but it is actually entirely covered with small chips of Selenite. Going further in to look at the mining pit, you can see why the mine owner doesn't want anyone to dig there out of season - not just because of his claim, but because the undercut has got deeper and deeper. The long seam of Selenite runs across the wall with dangerous boulders overhead, so as people dig out the Selenite underneath they aren't safely removing the overburden too, which could become dangerous and fall on someone as they're digging.
The owner mines and sells this Selenite as Utah Ice, for decorative use and to put in fishtanks! Interestingly the mine is actually not in Utah, but just over the border in Arizona. This particular deposit of Selenite is 240 million years old, and formed as part of the Moenkopi formation in the Triassic period. Selenite, like other forms of gypsum, forms as an evaporate mineral, much like the Halite we went to see earlier in the week. During the period of it's formation, a large basin covered much of the southwest portion of Utah and north western Arizona, which collected inflowing dissolved minerals over a long period of time. As the water evaporated from the basin, the minerals essentially collect together to form solid salts such as Gypsum, Calcite and Halite, as with Searles Lake and the Great Salt Lake.