Orthoclase belongs to the feldspar family of minerals, which also includes moonstone, amazonite, spectrolite and labradorite, Orthoclase is a transparent yellow feldspar resembling citrine quartz or yellow beryl, found primarily in Madagascar. It has a Mohs 6 - 6.5 so is most suitable for collectors or for pendants, earrings and pins. Yellow Orthoclase (Sanidine) is a little known gemstone that can be quite beautiful and a great collectors gemstone. It is sometimes referred to as "noble orthoclase". The hardness of orthoclase as a gemstone is on the softer side, being 6.0 to 6.5 on the mohs scale. The refractive index is 1.518 to 1.526 and the crystal system is monoclinic, prismatic. Gemstone mining occurs in Madagascar where it was first discovered in 1922 and to a lesser degree in Kenya and Myanmar.