Amethist ± 0.10 CT. 5x2.5 mm Marquise Cut Color: Fine Purple Clarity: Clean Luster: Astonishing Origin: Bolivia Hardness: 7 Specific Gravity: 2.65 - 2.91 Refractive Index: 1.544 - 1.553 Chemical Composition: SiO2, Silicon Dioxide Crystal Structure: Trigonal