If you like rich red rubies, it may in your best interest to learn how to tell a ruby apart from a garnet, a similarly colored yet much less expensive stone. Most jewelers can be counted on to be honest and provide you with a certificate of authenticity for your purchase. If you opt to purchase the gem online or from a private individual, however, you are more likely to fall victim to a scam. A ruby is a valuable stone, and ruby jewelry that can be passed down from generation to generation is well worth the added time and effort it takes to ensure authenticity.
Examine the coloring of the stone. A genuine ruby typically has a light red to medium red hue, whereas a garnet will be darker and have a burgundy or mahogany cast. In some cases, a ruby may also be mahogany, but it will always have a clarity that the dense, less refractive garnet does not.
Check the cut of the stone. Rubies most frequently have exotic cuts, such as a cushion or pear cut. The larger the ruby, the more unlikely it is to find it in a standard cut. So if you are examining a two-carat stone in a brilliant cut, the stone may be a garnet.
Hold the stone directly in front of your eye. The stone should be as close to your eye as possible without actually touching your eye.
Move the stone toward the light. Roll the stone around slowly between your fingers. Examine the light patterns that result within the stone. If you are holding a true ruby, you should see a rainbow pattern emerge in various shades of red and blue. A garnet, however, will display a rainbow pattern that contains greens and yellows.
Look for double rainbows. A ruby is a doubly refractive stone, so it refracts light in a much different way than a garnet, which is singly refractive. If you are holding a ruby, the rainbow image you see will be blurred and appear almost as one rainbow on top of another. The rainbow image you see within a garnet will be much more clear due to its singly refractive property.
Synthetic rubies have the same physical properties as genuine rubies. Because of this, you may be able to tell for certain that the stone you have is not a garnet, but it's still a good idea to have it examined under a microscope by a professional to determine if it is a genuine ruby.