Demantoid is a rare and highly prized variety of garnet known for its vibrant green color and exceptional brilliance. Here are some fun facts about demantoids:

1. Color and Brilliance: Demantoids are renowned for their intense green color, often described as emerald-green. They are also known for their remarkable dispersion, which is the ability to split light into its spectral colors, giving them a fiery appearance.

2. Garnet Family: Demantoid is a variety of the garnet family. Unlike most other garnets, which are known for red hues, demantoids stand out with their green color, making them one of the most sought-after garnet varieties.

3. Russian Origin: The most famous demantoid deposits are located in the Ural Mountains of Russia. Russian demantoids gained popularity in the late 19th and early 20th centuries when they were favored by European royalty and aristocracy.

4. Horsetail Inclusions: Demantoids are often valued for their unique and identifying inclusions called "horsetail inclusions." These are fine, golden, hair-like inclusions that resemble the tail of a horse. While they are technically considered flaws, they are prized by collectors for their distinctive appearance.

5. Andradite Garnet: Demantoid is a variety of andradite, which is one of the main species in the garnet group. Andradite garnets, in general, can also come in other color varieties, such as yellow-green (topazolite) and brown (melanite).

6. Demantoid from Other Locations: While Russian demantoids are the most famous, demantoid garnets have also been found in other locations, including Italy, Iran, Namibia, and Madagascar. However, Russian demantoids are often considered the most valuable due to their historical significance and unique inclusions.

7. Dispersion and Fire: Demantoids are known for their high dispersion, which means they exhibit a play of colors or "fire" similar to diamonds. This quality enhances their brilliance and makes them particularly attractive to gemstone enthusiasts.

8. Jewelry History: Demantoids have been used in jewelry for centuries, but they experienced a resurgence in popularity during the Art Nouveau period in the late 19th and early 20th centuries. Art Nouveau jewelers appreciated the demantoid's vivid color and incorporated it into intricate and nature-inspired designs.

9. Scarcity and Rarity: Due to their limited sources and the unique combination of color, brilliance, and horsetail inclusions, demantoids are considered one of the rarest and most valuable garnets.

10. Mohs Hardness: Demantoids have a hardness of 6.5 to 7 on the Mohs scale, making them suitable for most types of jewelry, but they require some care to prevent scratching.

Demantoids continue to be a gemstone of interest for collectors and jewelry enthusiasts, thanks to their stunning color, distinctive inclusions, and historical significance.