Beautiful Center-stone for an engagement Ring. Heated to enhance Luster and Color - The industry standard for Sapphire. Will make a Gorgeous Ring or Pendent accented with Diamonds. Color enhances to incandescent light. Gem with High Luster and Good Clarity. A Gem of Lasting Beauty. Refractive Index: 1.759-1.778 Hardness: 9 Chemical Comp: AL22O3 Density: 4.00 Crystal Group: Hexagonal The Sapphire belongs to the corundum group, with excellent hardness, exceeded only by Diamond –the hardest mineral on Earth. The oldest sapphire finds are in Ceylon, or Sri Lanka as it is known today where they are mined from ancient times. Ceylon sapphires are recognized by the luminosity of their light to mid-blue colors. Ranging from blue to purple and pink.