|Gem Type||Group||Hardness||Refractive Index||Specific Gravity|
Garnet is an unusual gem variety. It has the most diverse physical properties of any gem type. You may not be aware of it, but Garnet comes in nearly every color of the rainbow. We’re all familiar with the deep red gems but Garnets also come in yellow, orange, white, pink, green and purple. And because of the number of ways Garnets can form, it has a wide range of refractive indices and specific gravities. Whereas most gems will have a refractive index range of 1%, Garnet can vary from as low as 1.72 and as high as 1.88; that’s nearly 10%. Specific gravities are equally disparate ranging from 3.5 to 3.8. And to complicate matters further, many varieties of Garnet can blend. This often makes it very difficult to definitively say a gem is Rhodolite as opposed to Pyrope or Almandite, for example. That is why you’ll discover that most dealers will refer to anything in the red or violet range as simply “garnet”.There are certain varieties that stand out as unique. Grossular garnets are often light in color and come in
white, yellow, and green. The green variety is usually referred to as Tsavorite. This being the brightest of the colors and the most popular, it demands the highest prices within the group, but in actuality are no rarer than the yellow or white. Hessonite is also a Grossular Garnet and most commonly golden brown.
Another variety that is often golden brown but is more famous for beautiful Mandarin orange gems is called Spessartite. Its higher refractive index often shows itself in a little more brilliance in faceted gems. Most reddish brown gems in this category are blends with Almandite or Pyrope and are not usually sold as Spessartite. The closer the color is to a true orange, the higher the price. Super bright gems, sometimes even Padparadscha-like, are extremely rare.
Another green variety that stands out in the gem world is Demantoid. This Garnet has the highest refractive index and the highest specific gravity. It is noticeably more brilliant when faceted than Tsavorite and is significantly rarer, especially in large sizes. Demantoid is an Andradite Garnet which can be yellow, green or brown. Most fine Demantoid comes out of Russia but Andradite blends with yellow or olive tendencies can be found in many places.Garnet is a relatively common gem and most of the rough material is broken from massive chunks so you don’t always get to see the crystal structure. When you find crystals they are most often in dodecahedrons which remind you of futuristic geodesic dome architecture. They are often perfectly formed in all
directions and not clustered or twinned. This makes for some really neat crystal specimen.
The only synthetic Garnets are specialty varieties that don’t have any natural counterparts. They were some of the original Diamond simulants and are still popular for their amazing optical properties. These are Gadolinium Gallium Garnet (GGG) and Yttrium Aluminum Garnet (YAG).