Sapphire

The Logan Sapphire is displayed in the Smithsonian Museum of Natural History. At 423 carats, this blue sapphire is the largest one on public display. The name sapphire comes from the Greek word "sappheiros" for blue. Sapphire is a type of the mineral corundum. In fact, any gem-quality corundum is called sapphire unless it is deep red, and then it is called ruby. Corundum is Al2O3, and it is clear and transparent if there are no impurities. It has a refractive index of 1.76-1.78 and a hardness of 9. Its crystal symmetry is trigonal. A trace of chromium creates pink, iron creates green and yellow, chromium plus iron creates orange, and titanium plus iron creates blue. This blue sapphire color is difficult to render by a monitor, so the color has to be seen to be believed.

Sapphires and rubies exhibit double refraction, which resolves a beam of incident light into two beams which emerge with different colors. These two gems also sometimes exhibit a six-pointed "star" effect from reflection off microscopic, needle-shaped rutile crystals which intersect at 60° angles.

Myanmar (formerly Burma) is the major source of rubies and sapphires.

This is the Hall Sapphire and Diamond Necklace. It features 36 matched sapphires from Sri Lanka totaling 195 carats. Their deep sky-blue color contrasts brilliantly with a sparkling sea of 435 diamonds weighing 84 carats.

This is the Bismarck Sapphire Necklace with a 98.6 carat sapphire. The deep blue sapphire is surrounded by 312 diamonds.

Montana Sapphire Butterfly "Conchita". An 18k yellow gold brooch with 27.87 carats of sapphires. It is set with 333 fancy-colored Montana sapphires, most from the famed Rock Creek deposit.

Sapphire and diamond.

Mindat: Sapphire