|Rare Chrome Tourmaline
Chrome tourmaline is a rather special member of the tourmaline group. Found only in east Africa, it is usually found mainly in small sizes. But what it lacks in size it makes up for in color -- it displays perhaps the richest, most intense green in the gemstone world.
|Chrome Tourmaline Rough
There are many similarities between chrome tourmaline and tsavorite garnet. They are found in the same locations in Tanzania, and both are colored by chromium and vanadium. Miners will usually concentrate their attention on tsavorite, since it has more of an established market and fetches higher prices. But chrome tourmaline, while more scarce, is in many ways the equal of the finest tsavorite.
Chrome tourmaline is actually a distinct variety of tourmaline, called chrome dravite. Like emerald and tsavorite garnet, fine chrome tourmaline is a visually pure forest green with slightly yellowish to bluish secondary hues. The blue will normally show itself in incandescent light, the yellow will be more visible in daylight. A blue secondary hue is preferred to yellow.
Chrome tourmaline is distinguished from the more common and less vibrant green tourmaline by its chromium content. Collectors can test for chromium content with a Chelsea filter. Under the filter, chrome-laden stones will show flashes of red or orangy red. The common green tourmalines are colored by traces of iron. So when these stones are subjected to a Chelsea filter test, their color remains green.
Chrome tourmaline is quite rare in general, and it is particularly rare in sizes over one carat. A stone of fine quality over one carat is especially rare. Therefore, the collector should expect a large percentage increase in the price of stones in carat-plus sizes.
One reason that high quality chrome tourmaline is found mainly in smaller sizes is because the green color saturation is so high that larger stones can appear too dark, with a blackish tone. The smaller stones generally maintain the vivid, livelier color. Chrome tourmaline also looks best in daylight; some stones can look more opaque under incandescent lighting due to their dense color.