Tortoise shell is an organic gem material from the shell of the hawksbill sea turtle. It ranges from semitranspar- ent to translucent, with a mottled appearance that’s usu- ally yellow and brown, but occasionally black and white. For centuries, artisans used tortoise shell to make jewelry and other items, including combs and decora- tive furniture inlays. It was also a popular material for eyeglass frames and guitar picks.
Hawksbill turtles are an endangered species. Since the 1970s, they’ve been protected under the UN Convention on International Trade in Endangered Species of Fauna and Flora (CITES). Most of the more than 100 countries that are parties to the convention also have supporting laws or regulations that ban commerce in tortoise shell.
US federal law prohibits the import or sale of items made from hawksbill shell, unless they can be proven to be at least 100 years old. Pieces that aren’t that old, but were made and privately owned before 1974, can be legally purchased from individuals or estates, but only for a collection, and not for resale.
Hardness & Toughness
Hardness 21/2on Mohs scale
Stability
Environmental Factor Reaction
Heat Softens at the temperature of boiling water; high heat darkens, then burns the material
Light May darken with age Chemicals Attacked by nitric acid
Treatments
Treatment Purpose Stability Prevalence Detection Occasional
* If there is any doubt, send the gem to a gemological laboratory for verification.
Care and Cleaning
Type of Cleaning Advisability Ultrasonic cleaning Never
Steam cleaning Never
Warm, soapy water Safe, but hard-bristle brushes can leave scratches
Imitations
PlasticAlternatives
Agate Amber Sardonyx Shell Lamination (pieces are soft- ened and joined together with heat and pres- sure) Made thicker material for carving Variable, depending on how well the layers were joined Detectable by a trained gemolo- gist or gemologi- cal laboratory*Tourmaline
People have probably used tourmaline as a gem for centuries, but until the development of modern mineralogy, they identified it as some other stone (ruby, sapphire, emerald, and so forth) based on its color. Portuguese explorers, for example, discovered deposits of green tourmaline in Brazil in the mid- 1500s, but they thought it was emerald.
The confusion about the stone’s identity is even reflected in its name, which comes from toramalli, which means “mixed gems” in Sinhalese (a language of Sri Lanka).
In the late 1800s, tourmaline became known as an American gem through the efforts of Tiffany gemologist George F. Kunz. He wrote about the tour- maline deposits of Maine and California, and praised the stones they pro- duced. In spite of its American roots, tourmaline’s biggest market was in China, where the imperial court prized tourmaline as a material for small carvings and utilitarian objects like snuff bottles.
The supply of tourmaline began to expand during the first half of the twentieth century, when Brazil yielded some large deposits. Then, beginning in the 1950s, additional finds appeared in countries around the world. Tourmalines come in a wide variety of exciting col- ors. In fact, tourmaline has one of the widest color ranges of any gem species. It occurs in various shades of almost every hue, and there are a number of trade names for its color varieties:
• Rubellite—pink, red, purplish red, orangy red, or brownish red. (Some in the trade argue that pink tourmaline shouldn’t be called rubellite.)
• Indicolite—dark violetish blue, blue, and greenish blue.
• Paraíba tourmaline—intense violetish blue, greenish blue, or blue from the state of Paraíba, Brazil. (This variety was discovered in 1988.)
• Parti-colored tourmaline—tourmaline with more than one color. One of the most common combinations is green and pink, but many others are possible.
• Watermelon tourmaline— pink in the center and green around the out- side. Crystals of this material typically have a pink core surrounded by green, and they’re cut in slices.
Some tourmalines also show chatoyancy. Cat’s-eye tourmalines are most often green, blue, or pink, with an eye that’s softer and more diffused than the eye in fine cat’s-eye chrysoberyl. This is because, in tourmaline, the effect is caused by thin tube-like inclusions that occur naturally during the gem’s growth. The inclusions are larger than the inclusions in cat’s-eye chrysoberyl, so the chatoyancy isn’t as sharp. Like other cat’s-eyes, these stones have to be cut as cabochons to bring out the effect.
Sources
Afghanistan
Brazil Major source Kenya Madagascar Mozambique Myanmar (Burma) Namibia Pakistan Russia United States
Hardness & Toughness
Hardness 7 to 71/2on Mohs scale
Toughness Fair
Stability
Environmental Factor Reaction
Heat High heat can alter color; sudden temperature change can cause frac- turing
Light Generally stable Chemicals None
Treatments
Treatment Purpose Stability Prevalence Detection Heat Stable Common Undetectable
Irradiation Undetectable
Acid Stable Occasional Undetectable
Occasional
* If there is any doubt, send the gem to a gemological laboratory for verification.
Care and Cleaning
Type of Cleaning Advisability Ultrasonic cleaning Risky
Steam cleaning Risky Lightens very dark green or blue-green stones; converts brownish purple stones to “rose” pink; produces bright greenish blue to yellowish green stones from grayish Paraíba material Produces deep pink, red, or pur- ple from very light pink, green, blue, or colorless material; converts some light yellow or green material to a darker yellow or orange; turns some green stones into red and green parti- colored
Common for pink, red, and purple. Occasional for yellow, orange, and parti-color. Fair to good.
Color may fade under high heat or very prolonged exposure to bright light. Improves the appearance of cat’s-eye stones
Fair. Heat and solvents can dam- age or destroy the sealant.
Prevents dirt from getting into the tubes that cause the cat’s-eye effect Sealing tubes in cat’s-eye material with plastic or epoxy resin Detectable by a trained gemolo- gist or gemologi- cal laboratory*
Imitations
Glass Synthetic ruby Synthetic sapphire Synthetic spinelAlternatives
Almandite garnet Amber Amethyst Aquamarine Cat’s-eye chrysoberyl Chrysoberyl Citrine Emerald Fire opal Kunzite Malaya garnet Morganite Peridot Pyrope garnet Rhodolite garnet Ruby Sapphire Smoky quartz Spessartite garnet Spinel Tanzanite Topaz Tsavorite garnet ZirconFreshwater cultured pearl torsade with decorative clasp featuring tourmaline slices.