Amazonite is a variety of microcline feldspar. It is usually blue or green. Colorado amazonite is special because it can appear as well-formed crystals, as opposed to the formless shapes found elsewhere in the world. The crystals can also be very large.
Much of Colorado's amazonite can be found in the Pikes Peak granite. The granite provides the lead inclusions that color the microcline blue instead of pink. The Crystal Peak area between Woodland Park and Lake George is famous for its amazonite and other crystals, but it is now mostly private land and cannot be hunted.