Quartz is the most common mineral of all. It is a form of silica. You can find Quartz that is transparent, or milky or translucent. There are also more varieties of Quartz than any other mineral. Some of the varieties are familiar names, such as Amethyst, Citrine and Agate. Rock collectors enjoy the hexagonal crystals which can be quite large. 
A large piece of rock Quartz with hexagonal transparent and translucent crystals
Clusters of tiny crystals are known as “drusy quartz.” The most commonly seen chunks of quartz in Arizona are milky white and massive (not crystalline), also known as “bull quartz.”
A large chunk of milky Quartz
Arizona prospectors have long looked to Quartz as a possible sign of gold. Some Quartz veins may have gold filling the fractures in the Quartz. Sometimes gold is hidden in pockets of sulfide minerals such as pyrite in the Quartz. Gold panners sift through sand, which contains lots of Quartz, to sort out the heavy bits of gold from the debris.
Why is Arizona so... 
The K-12 education programs at the former Arizona Mining and Mineral Museum served nearly 50,000 students a year until the Arizona Historical Society gained control of it and destroyed it. Complete details are available on the blog Mineral Museum Madness.
Good point. An unfortunate decision was made when the choice was made to house a new museum in the Mining Museum building and then did not have funds to even begin. Such a waste of a wonderful resource that was being well used.