Generally, gemstone-quality corundum in all shades of red, including pink, are called rubies. Furthermore, rubies can show color changes-though this occurs very rarely-as well as chatoyancy or the "cat's eye" effect. This is one example where inclusions increase the value of a gemstone. Such effects occur when light is reflected off the "silk" (the structurally oriented rutile needle inclusions) in a certain way. Asterisms are best visible with a single-light source and move across the stone as the light moves or the stone is rotated. These rubies are cut into cabochons to display the effect properly. Some rubies show a three-point or six-point asterism or "star". Untreated rubies of high quality command a large premium. These days, almost all rubies are treated in some form, with heat treatment being the most common practice. Usually, the rough stone is heated before cutting.
Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, or substitutes. By arranging mirrors or other means to pass emitted light repeatedly through the crystal, a ruby laser in this way produces a very high intensity of coherent red light.Īll natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as "silk". If 694-nanometer photons pass through the crystal during that time, they can stimulate more fluorescent photons to be emitted in-phase with them, thus strengthening the intensity of that red light. Theodore Maiman says that "because of the low chromium level in these crystals they display a lighter red color than gemstone ruby and are referred to as pink ruby." Īfter absorbing short-wavelength light, there is a short interval of time when the crystal lattice of ruby is in an excited state before fluorescence occurs. The chromium concentration in artificial rubies can be adjusted (in the crystal growth process) to be ten to twenty times less than in the natural gemstones. Additionally, absorption at any of the above wavelengths stimulates fluorescent emission of 694-nanometer-wavelength red light, which adds to its red color and perceived luster. If one percent of the aluminium ions are replaced by chromium in ruby, the yellow-green absorption results in a red color for the gem. Note the two broad violet and yellow-green absorption bands and one narrow absorption band at the wavelength of 694 nm, which is the wavelength of the ruby laser. Transmittance of ruby in optical and near-IR spectra. The world's most valuable ruby to be sold at auction is the Sunrise Ruby.
Ruby is the traditional birthstone for July and is usually pinker than garnet, although some rhodolite garnets have a similar pinkish hue to most rubies. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions may indicate that the stone has been treated. The brightest and most valuable shade of red called blood-red or pigeon blood, commands a large premium over other rubies of similar quality. The quality of a ruby is determined by its color, cut, and clarity, which, along with carat weight, affect its value. Some gemstones that are popularly or historically called rubies, such as the Black Prince's Ruby in the British Imperial State Crown, are actually spinels.
The color of a ruby is due to the element chromium. The word ruby comes from ruber, Latin for red. Ruby is one of the traditional cardinal gems, alongside amethyst, sapphire, emerald, and diamond. Other varieties of gem-quality corundum are called sapphires. Ruby is one of the most popular traditional jewelry gems and is very durable. A ruby is a pink-ish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide).