Moonstoneis a sodium potassium aluminium silicate with the chemical formula (Na,K)AlSi3O8 and belongs to the feldspar group. Its name is derived from a visual effect, sheen or schiller (play of color), caused by light diffraction within a micro-structure consisting of regular exsolution layers (lamellae) of different alkali feldspars (orthoclase and sodium-rich plagioclase).
The most common moonstone is of the orthoclase feldspar mineral adularia, named for an early mining site near Mt. Adular in Switzerland, now the town of St. Gotthard. Solid solution of the plagioclase feldspar oligoclase +/- the potassium feldspar orthoclase also produces moonstone specimens.
Moonstone is a stone of protection. Brings hope and enhances sensitivity, intuition and psychic abilities.