
Tourmaline, a gem not widely known to gem
buyers, displays the most dazzling and surpassing variety of colors of all known
gemstones. Some crystals may display two or three color bands along their length, or
show complex concentric zoning in cross section. Some o fthe most delicate, subtle,
and exquisite colors in the mineral kingdom belong to the tourmaline group.
Tourmaline is actually a general group term
that applies to several minerals with similar atomic structures and chemical compositions.
Confusion sometimes arises because there are mineral species names (elbaite, schorl, and
dravite) and names for color varieties: rubellite (pink and red), indicolite (blue),
achroite (colorless), siberite (reddish-violet), and dravite (brown).
Tourmaline is available in the trade in large
quantities and in a huge array of colors, yet it seems less well known than other gems.
Tourmalines are hard and durable and make fine ringstones, especially when set with small
diamonds. The price ranges from a few dollars per carat to more than $300 per carat,
with large, flawless gems commanding the premium prices. Brazil produces most of the
green and blue-green gems seen on the market, but occasional stones from other sources may
be available to certain times and places.
Color determines price among tourmalines; the
most desirable colors are a green resembling the color of fine emerald, characteristic of
chrome-tourmaline, and lively pale-green shades, as well as the rich reddish-pink of fine
rubellite. Flawed stones of any color are less desirable and less expensive than
"clean" stones, except in the case of almost never completely free of inclusions
or minor internal flaws.
Synthetic gems created to resemble tourmaline
cannot be distinguished easily with the naked eye. Such synthetics are commonly
found in jewelry today, since tourmaline is the alternate birthstone for October.
The authenticity of a tourmaline should therefore always be checked before purchase.