There is nothing quite like a brilliantly-hued gem to catch someone’s eye, and the oxide mineral known as corundum is certainly capable of producing its share of colorful gems. A form of aluminum oxide, corundum is naturally clear and very hard, with the ability to scratch almost every other mineral. More importantly, when appearing as pink-orange, red, or blue, corundum gives us padparadscha, rubies, and sapphires.
Padparadscha: Pinkish-orange hued corundum originally found in Sri Lanka but also present in Vietnam and East Africa. These gems are extremely rare, particularly those with no artificial treatment. The name itself comes from Sanskrit for “lotus” and “color”.
Rubies: Red-hued corundum (the color is caused by chromium) considered to be one of the four precious stones (rubies, sapphires, emeralds, and diamonds). Prices of rubies are actually determined by their color, with the most expensive ones being blood-red in appearance. Like diamonds, cut, carat, and clarity can also affect the price, along with size and geographic origin.
Sapphires: Blue corundum that can also be found in shades of gray and black. Like rubies, size and origin also have an effect on the price of the gem. They are also judged based on hue, saturation, and tone, with hue being the “color”, saturation the vividness of the hue, and tone the lightness of the hue. One of the largest gem-quality blue sapphires in existence currently resides in the National Museum of Natural History in DC – the Logan Sapphire.