Most people think of garnets as a beautiful red stone that is mainly known for being January's birthstone. However, there are actually many different types of garnet that range in value from fairly inexpensive to nearly priceless and in color from deep red to a brilliant green. There are several ways to determine what type of garnet you are dealing with.
Evaluate the color. The most obvious way to tell garnets apart is their color. Traditional garnets are red and often called rhodelite while tsavorite and demantoid garnets are green. Some types of rare garnet are a fiery orange color and they can even come in natural, earthy browns.
Consider the brilliance. Garnets tend to be brilliant stones despite their generally relatively low price. However, some types are more brilliant than others. Demantoid garnets, for example, sparkle even in very dim light. Spessarites, which tend to be yellowish or orange also have a great deal of brilliance.
Look for inclusions. Some types of garnet are identified by their inclusions. For example, demantoid garnets have long, feathery inclusions called "horsetail inclusions." They actually make the stone brighter and more valuable.
Find out where the stone is from. This will tell you a lot about what type of garnet you have. Rhodelites and other fairly common garnets may be found in mines throughout the world. However, demantoid garnets come from Russia and sometimes Nambia, while mandarin garnets are found almost exclusively in Nambia and Nigeria.
Check for hardness. Garnets are extremely hard, and rarer types like demantoid and mandarin are even harder than rhodelites and verdelites. If a stone is extremely hard or has been cut with very intricate facets (usually reserved for harder stones) then you may have a less common garnet on your hands.