Moonstone; the June Birthstone  Moonstone is one of the three colorful stones used to celebrate the month of June in the gemstone world alongside pearls and alexandrite. This popular gemstone belongs to the feldspar group of minerals and is composed of orthoclase feldspar with a small amount of albite feldspar. It has a chemical formula of (Na,K)AlSi3O8, where Na and K represent the sodium and potassium ions that substitute for