Citrine is a form of quartz with ferric iron impurities. It is named for its yellow lemon color that ranges from yellow to amber, to orange and brown. It is rarely found naturally. Most of the citrine gemstones available today are produced artificially. It has an index refraction of 1.544 to 1.553, a birefringence of 0.009, and a hardness of 7. It has no cleavege, making it less susceptible to breaking or cracking.