Sapphire
Gemstone
Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide with trace amounts of elements such as iron, titanium, cobalt, lead, chromium, vanadium, magnesium, boron, and silicon. Wikipedia
Hardness (Mohs hardness scale): ≥ 9
Associated month: September
Chemical formula: Al₂O₃
Refractive index: 1.76 – 1.77
Luster: Vitreous and Adamantine
Density: 3.98 g/cc