Top Quality, One of a kind. With Algt Antwerp Certificate. Species ........................................................................ Natural Corundum Variety .............................................................................................. Sapphire DESCRIPTION Shape & Cutting Style ............................................... Oval, Mixed Cut Measurements ................................................. 6.66 x 5.90 x 4.04 mm Carat Weight ............................................................................. 1.51 Carat Color .................................................................... Intense Blue (Greenish) Transparency ......................................................................... Transparent Indications of heating present. Chemical Composition ................................................................. Al2O3 Crystal System .......................................................................... Trigonal Mohs Hardness ................................................................................... 9.0 Specific Gravity ..................................................... 3.97 - 4.10 g/cm3 Optical Character .................................................................... UniaxialRefractive Index ............................................................ 1.757 - 1.779 Birefringence ................................................................... 0.008 - 0.009 I cut gemstones , collect, and Trade only top quality. I have study to cut and trade opals and color gemstones in IGS. Don't like? Welcome to return and have your money back. Shipped with insurance, tracking and express shipping. Please see my other Auctions.