Next to ruby and the rare red diamond, spinel is the most expensive of all red gems, commanding prices as high as $2,000 per carat for stones above one carat in weight. (One carat equals one-fifth of a gram.) Class: semiprecious Origin of Name: probably from the Latin spina (thorn) Color: red, orange, brown, green, blue, violet, clear Chemical Composition: magnesium aluminum oxide Crystal System: cubic Hardness: 8 Specific Gravity: 3.58-4.06 Geographic Origins: Sri Lanka, Burma, Brazil Next Photo: ©International Colored Gemstone Association 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