Blue Sapphire

Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminum oxide (alpha-Al2O3) with trace amounts of elements
such as iron, titanium, chromium, copper, or magnesium. The 423-carat (84.6 g) Logan
sapphire in the National Museum of Natural History, in Washington, D.C., is one of the largest faceted gem-quality blue sapphires in existence.