Yellow Sapphires : Important Things You Need To Know Chemical Formula                                                   AL2O3 Color                                                                          Yellow Hardness                                                                   9 Crystal System                                                         Hexagonal Refractive Index                                                       1.76 – 1.77 Specific Gravity                                                        3.9 – 4.1 Transparency                                                           Transparent to Opaque Double Refraction                                                   0.0008 Luster                                                                        Vitreous to adamantine Cleavage                                                                  None, but may exhibit parting Mineral Class                                                           Corundum   Yellow Sapphire known as […]