What Is Moonstone & How To Use It? A gemstone that shimmers like lunar beams, "What Is Moonstone" and how to use it, Let's see it is an oligoclase or orthoclase feldspar (which is a mineral group) gemstone. Made up of sodium potassium aluminum silicate, moonstone has a pearly opalescent look. In simple terms, moonstones are a type of feldspar that are filled with alternating layers of oligoclase or orthoclase and albite.