Chrome Tourmaline
Chrome tourmaline is a rare type of dravite tourmaline from East Africa. It's a vivid green hue is produced by trace amounts of chromium and vanadium atoms in the crystal; these are the same elements that produce the pure green colors in emeralds and tsavorite garnets.
Like emerald and tsavorite garnet, fine chrome tourmaline is a visually pure "forest" green with slightly yellowish to bluish secondary hues. The finest examples of chrome tourmalines resemble fine emeralds and tsavorites.
Good, large crystals of chrome tourmaline are very rare because of the tendency of the gem to appear nearly opaque in larger sized specimens. The opaque appearance is because chrome tourmaline tends to have a grey or black overtone.
"Chrome tourmaline is quite rare generally, and particularly rare in sizes over one carat. A stone of fine quality over one carat is very rare. Therefore, the collector should expect a large percentage increase in the price of stones in carat-plus sizes. The next jump in rarity occurs at five carats. Stones of fine quality above ten carats are extremely rare, so rare in fact that I have never seen one." (as quoted from Richard W. Wise on the website: Ganoksin, The Gem and Jewelry World's foremost Resource on the Internet)
