GARNET COLOURS
Garnets come in lots of colors and from various origins. They are a broad category of gem with a broad category of value and color.
For example, almost radiant, almost always foiled, are garnets from France called Perpignan, named after the area in France from whence they hailed. Perpignan garnets have an amazing shine and luster. Want some? Not easily possible as they are mined out and the only perpignan garnets to be found are in antique jewelry. 
Green garnets, especially demantoids, originally found in the Ural Mountains of Russia, are highly desireable and often command prices greater than diamonds. Their bright, almost electric colour is quite unforgettable and I've seen collectors salivate at the thought of them.
They are a similar green to peridot, which is not in the same league as demantoid garnets.
Demantoid garnets are very rarely found greater than a carat and as the size increases, the price and value is exponentially higher. Today, demantoids are found in various locations, but for quality and price, look for antique Russian demantoid garnets.
#5414 
Another green garnet of an entirely different shade is the tsavorite, only discovered in the last quarter of the 20th century. It's gorgeous, but don't confuse tsavorites with emeralds. While tsavorites are expensive garnets (and prices rising all the time), they are not yet in the same price category as emeralds. Maybe soon..
#6836
We are not going to become geologists or chemists, but it is useful to understand that the different colors of garnets are the result of different elements inside the gem.
Almandine garnets are that fireball red that we associate with carbuncles and Bohemian jewels of the 19th century. It is the most common type of garnet.
Pyrope is pinker and purer than Almandine.
Rhodolite is purple and a mixture of Almandine and Pyrope.
Spessartite is orange.
Pyrope (magnesium aluminum silicate)
Spessartite (manganese aluminum silicate)
Almandine (iron aluminum silicate)
Grossular (calcium aluminum silicate)
#7298 orange and green garnet necklace
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