For this week’s gemstone highlight, I thought we could continue along the mystical moon vein started last week by taking a look at the moonstone. All hallows’ eve is coming up soon, after all. Geology | Origins of a Gemstone Moonstone originates from the “potassium aluminosilicate” variety of the large mineral group of feldspars. With feldspar making up over half of the Earth’s crust composition, it’s likely that you could pick up a rock anywhere in the world, and it would probably contain at least one mineral from the feldspar group (University of Minnesota, Potassium Feldspar). In its rough form, potassium feldspars typically form pink, reddish or white, hard blocky crystal masses. The potassium feldspar series has its own sub-varieties, including: orthoclase, sanidine, oglioclase and microcline. Moonstone is typically cut from the sanidine or orthoclase. Sanidine is a high temperature form of potassium feldspar and has a less ordered crystal structure than orthoclase. It is primarily found in volcanic igneous rocks where magmas cooled more rapidly and crystals have less time to form, resulting in …