Spodumene, a lithium aluminum silicate, is one of the very few gemstones
containing lithium. It has had more importance as a gemstone in the
United States than elsewhere, a situation due to early discoveries of
unique occurrences of a lavender-pink variety at Branchville, Conn., in
1879 and in San Diego County, Calif, about 20 years later. At the time
of the discovery of the California material, the variety was named
_kunzite_ in honor of G. F. Kunz, a noted American gemologist of the
times.
[Illustration: The 177-carat kunzite (at lower left) is a large
flawless stone cut from California material of this variety of
spodumene. It was given to the Smithsonian Institution by the
American Gem Society. The other stones, all from Brazil, represent
the more usual shades of spodumene. They weigh 327 carats (top
left), 256 carats (top right), and 69 carats. (About half actual
size.)]
The finding of a bright green variety, _hiddenite_, in North Carolina
about 1880 greatly stimulated the interest of American gem collectors.
Some of the bright green spodumene coming from Brazil in recent years
compares very favorably in color with North Carolina hiddenite. Other
than in a scattered few of these unusual occurrences of kunzite and
hiddenite, spodumene usually is found in yellow and yellow-green shades,
with Brazil and Madagascar being the chief sources.
[Illustration: This 880-carat kunzite from Brazil is one of the
largest stones of its kind. (About actual size.)]
Spodumene has a hardness of about 7, but with a refractive index of
about 1.66 and a low dispersion there seems to be relatively little to
recommend it as a gemstone. The fact that it exhibits a very strong
tendency to cleave in two different directions would seem to rule it out
completely as being too difficult to cut. Nevertheless, the production
and purchase of cut stones of spodumene persist because of the beauty of
the gem.
The kunzite and hiddenite varieties of spodumene show strong
_pleochroism_, or the ability to show three different colors when viewed
in the direction of different axes. Some of the large Brazilian kunzite
crystals mined in the early 1960’s have an intense rose-violet color
when viewed along the long axis of the crystal but have pale blue-violet
and pale tan colors when viewed from the other two directions. When heat
treated, or exposed to strong light, this Brazilian kunzite loses its
tan and bluish colors but retains the intense rose-violet. Because of
spodumene’s pleochroism, the direction of cutting in the stones becomes
extremely important, as it must be done in a manner that will take
advantage of the violet color in kunzite and the green color in
hiddenite.
VARIETIES
Kunzite: Lavender violet to rose violet
Hiddenite: Deep green