Feldspar bead is a crystalline rock that contains different amounts of silica and alumina. Feldspars are divided into two groups: Potassium feldspars and Plagioclase feldspars. Potassium feldspars are known for their high refractive index, making them clear and shiny. They are very hard and brittle, making them ideal for high-precision applications. Plagioclase feldspars are known for their low refractive index, making them translucent and soft. It is the most common mineral found in igneous rocks. The mineral can be found in metamorphic rocks as well and some of the best examples include marble, granite, and quartzite.