Moonstone is a member of the feldspars, the most abundant mineral group in the Earth's crust. The stone is famous for its pearly blue opalescence and bronzy iridescent luster. Class: semiprecious Origin of Name: named for its pearly luster, reminiscent of the Moon Color: colorless, white to yellowish grey, reddish to bluish grey Chemical Composition: potassium aluminum silicate Crystal System: monoclinic Hardness: 6 Specific Gravity: 2.56-2.59 Geographic Origins: Sri Lanka, India, Madagascar, Burma, Tanzania, Colorado, Indiana, New Mexico, New York, North Carolina, Pennsylvania, Virginia, Wisconsin Next Photo: ©International Colored Gemstone Association/Bart Curren The Science Behind the Sparkle | Diamonds in the Sky A Primer of Gemstones | See Inside a Diamond Resources | Transcript | Site Map | Diamond Deception Home Editor's Picks | Previous Sites | Join Us/E-mail | TV/Web Schedule About NOVA | Teachers | Site Map | Shop | Jobs | Search | To print PBS Online | NOVA Online | WGBH © | Updated November 2000