Whether it’s understanding gemological or jewelry terms in an article you’re reading or simply gaining a greater understanding of the world of jewelry and gemstones, our Jewelry & Gem Dictionary is a handy reference guide. And, unlike most dictionaries, ours makes for interesting reading all on its own!

Tabasheer (also spelled tabashir) or pearl opal is an organic stone that forms in damaged joints (nodes) of bamboo plants. This hydrated form of silica appears as a rounded mass of opal, and looks like seed pearls.

The table is the large, flat area at the top of a cut gemstone.

Tahitian pearls (also called black pearls) are dark-colored pearls. They are produced by the large, black-lipped pearl oyster Pinctada margaritifera (also called the Tahitian black pearl oyster), a mollusk found in the tropical Indo-Pacific Ocean. Black pearls come in many colors, including many body shades and overtone tints including gray (light gray to almost black), peacock green (especially valuable), aubergine (eggplant), and deep brown. The color of the dark nacre is determined by the minerals in the oyster’s diet (plankton) and in its environment. Many “black pearls” are dyed or irridiated to enhance or change their color; it is difficult to tell a natural pearl from a treated pearl. Tahitian pearls are graded on six factors: 1.Shape (round is most valued), 2.Size (the larger the better), 3.Surface Quality= (clean is superior to blemished), 4.Luster (the more high-gloss luster the better), 5.Nacre Thickness (thicker is better and longer lasting), and 6.Color (overtones atop the body color add value to the pearl. The most sought-after color is peacock green and darker colors are more valuable Overtone colors include blue, pink, gold, silver, aubergine, and peacock green).

Tanvorite is a trademarked name for a manmade gemstone. This synthetic stone is a deep blue-purple stone that resembles tanzanite.

Tanzanite (strontium-rich Calcium-aluminum silicate) is a valuable, transparent, blue-violet type of zoisite resembling sapphire. Tanzanite has a hardness of 6 and a specific gravity of 3.35. It is often heat-treated in order to produce a deeper blue-violet color. This mineral was discovered in 1967 by Manuel d’Souza (an Indian tailor) southwest of Mt. Kilimanjaro in Tanzania, Africa.

Taxco is a town in the State of Guerrero in Mexico that is famous for its silver jewelry production. The American silversmith William Spratling, set up shop in Taxco in 1929, and many other silversmiths followed. Early Taxco jewelry is avidly collected. Modern pieces are distinguished by a registration mark of two letters followed by a series of numbers (this mark was required by the Mexican government since 1979).

To temper is to strengthen or harden metal (or glass) by heating it or by heating then cooling it. Harder tempers are stronger, more spring-like, and brittler (when they are bent, they may break). Softer tempers are weaker but bend easily.

A tennis bracelet is a simple, flexible, in-line diamond bracelet. The name tennis bracelet was first used when the great tennis player Chris Evert dropped a diamond bracelet during a tennis match in the summer of 1987 (at the US Open Tennis Tournament). She had to stop the match until she found her bracelet. Since then, that style of bracelet has been called a tennis bracelet.

Thermoluminescent minerals emit bright light when heated. For example, chlorophane is a varity of fluorite that emits bright green light when heated.

Thermoset plastic (also known as thermoplastic) is a hard, non-rigid synthetic substance that cannot be melted by reheating. Thermoset plastic is formed under high heat or pressure by a process known as polycondensation. Bakelite is a thermoset plastic. The bangle above is “butterscotch” bakelite.

The Tiffany setting is a ring with a high, six-pronged solitaire diamond on a simple circular band. This design was introduced by Tiffany & Co. in 1886.

Tiger’s eye is a yellowish-brown to reddish-brown gemstone that has a silky luster. This gemstone has bands of yellow and brown; when viewed from the opposite direction, the colors are reversed. Tiger’s eye is usually highly polished and set as a cabochon (or cut as a bead) to display the stone’s chatoyancy (light reflected in thin bands within the stone). Tiger’s eye is a type of chatoyant quartz with fibrous inclusions (especially crocidolite). This stone is sometimes heat-treated. Tiger’s eye has a hardness of 7.0. Most tiger’s eye is mined in South Africa, but it is also found in Australia, Brazil, Burma (Myanmar), India, Namibia, Sri Lanka (Ceylon), and the USA. Green-grey varieties of this stones are called cat’s-eye quartz. Blue-grey to bluish varieties are called hawk’s-eye. Deep brown varieties of this stone are called bull’s-eye or ox-eye.

A toggle clasp (also called a bar and ring clasp) is a jewelry fastener in which a bar can be inserted into a ring to fasten a piece of jewelry. It is used to attach the two ends of a necklace or bracelet.

Topaz (aluminum silicate fluoride hydroxide) is a very hard gemstone that ranges in color from brown, to yellow to blue to pink. Pink topaz is usually created by irradiating common yellow topaz. Other colors are often created by heat-treating and/or irradiating topaz. Imperial topaz is golden orange-yellow topaz; it is the most valuable topaz Topaz has a hardness of 8 and a specific gravity of 3.5-3.6. Topaz may have been named for the legendary Topasos Island in the Red Sea.

A torque (also spelled torc) is a necklace that consists of a narrow, twisted band made of metal. This type of ornament was worn by the ancient Celts, Britons, and Gauls.

A torsade is a necklace made of many strands that are twisted together.

Tortoise shell is the shell of a tortoise. It was used in the 1800’s for jewelry, hair combs, and other ornaments but is banned today. Tortoise shell inlaid with precious metals is called pique. Tortoise shell will burn easily, and smells like burning hair. It is easily imitated by plastic, but its smell when burnt is very different. Tortoise shell has a hardness of 2.5 and a specific gravity of 1.29.

Tourmaline is a dichroic gemstone that comes in many, many different colors; it also appears to have different colors depending on the angle at which it is seen. Tourmaline has the greatest color range of any gemstone – thel ighter colors are more valuable than the darker colors. It ranges in color from pink to green to red (rubellite) to purple to blue-green (indicolite) to colorless (achroite) to black. Watermelon tourmaline is both pink and green. Tourmaline occurs as an elongate three-sided prism and is mined in Brazil, The Ural mountains in Russia, Namibia, Sri Lanka, and California. Tourmaline was only discovered in the 1700’s. Tourmaline has a hardness of 7-7.5 and a specific gravity of 3.02-3.25. It is doubly-refractive.

Tourmalinated quartz is a variety of transparent quartz that has needle-like inclusions of black to dark green tourmaline crystals. This beautiful stone is found worldwide. Tourmalinated quartz has a hardness of 7.0. This stone is not enhanced.

Translucent materials allow light to pass through them, but the light is diffused (scattered). Some translucent stones include moonstones, opals, and carnelian. Lucite and other plastics can also be translucent.

Transparent materials allow light to pass through them without diffusing (scattering) the light. Some translucent stones include diamond, zircon, emerald, rock crystal, and ruby. Plastics like lucite can also be transparent. In the confetti lucite bangle above, the glitter within the lucite is visible.

Transvaal jade is not jade; it is a green to gray massive variety of grossular garnet, calcium-aluminum silicate. It is found about 40 miles west of Pretoria, South Africa. Transvaal jade can be distinguished from jadeite or nephrite by its high refractive index. Grossular garnet has a refractive index of 1.72 to 1.73, a hardness of 6-7.5 and a specific gravity of 3.5 – 3.67.

Trap rock is a type of igneous rock. This solidified lava often contains pockets of crystals.

Trapiche emeralds are rare, valuable emeralds that have a black, six-rayed star within them, caused by black carbon impurities (the star is not an asterism). These stones are usually cabochon cut to display the beautiful spoke-like star. These stones are only mined in Colombia, South America. Trapiche emeralds are sometimes called star emeralds (but the term star emerald can also refer to emeralds with an asterism). Trapiche is a Spanish word for the spoked wheel that is used to grind sugar cane.

A trembler is a piece of jewelry that has a part (or parts) set on a spring; the spring-set parts move as the wearer of the jewelry moves.

Trifari is a pre-eminent jewelry manufacturing company that produces high-quality and beautifully-designed pieces. The company began as Trifari and Trifari in 1910, founded by Gustavo Trifari and his uncle; a few years later, his uncle left and the company was simply Trifari. Leo Krussman joined Trifari in 1917. In 1918, when Carl Fishel joined the company, they renamed the company Trifari, Krussman and Fishel (their hallmark was T.F.K.). Alfred Philippe, who had been a jewelry designer for Cartier and Van Cleef & Arpels, designed pieces for Trifari for many years. Some other Trifari designers included Jean Paris (1958 -1965), Andre Boeut (1967 – 1979), and Diane Love (1971 – 1974). Trifari was owned by the Hallmark Company from 1975-1988, and by Crystal Brands from 1988-1994. It was then part of the Chase Capital division of the Monet Group, which later went bankrupt and was bought by Liz Claiborne (2000). The classic pin and earrings set above has paste rubies, emeralds, sapphires, and diamonds (and was designed by Alfred Philippe, about 1947-8).

The trillion cut is a triangular cut based upon a brilliant style cut (and not a stepped facet). The corners of the triangle are truncated (cut short) and there are a variety of facets, giving this cut a sparkling brilliance.

A triplet is a manufactured stone that is made by sandwiching three thin layers of stones together. For example, an opal triplet had a top, protective layer of clear quartz, a thin middle layer of opal, and a base layer of dark, color-enhancing matrix (usually black onyx or ironstone).

Precious metals (like gold, platinum, and silver) are measured in troy weight, which has units of pennyweights, ounces, and pounds. Troy ounces and pounds are different from everyday US measures.

1 pennyweight 24 grains = 1.5552 grams
1 Troy ounce = 20 pennyweight 31.1035 grams
1 Troy pound = 12 Troy ounces 373.24 grams
Tsavorite is a rare, deep green variety of grossular garnet, a type of garnet, calcium-aluminum silicate. The emerald green color comes from vanadium and chromium. Tsavorite is similar to emerald, but is rarer and more durable; it also has a higher refractive index, 1.74. Tsavorite stones over two carats are considered large and are very rare. Tsavorite has a hardness of 7.5 and a specific gravity of 3.6. Tsavorite is found in east Africa; it was named by Harry B. Platt of Tiffany & Co. for the Tsavo National Park in Kenya, where this gemstone was originally found in 1967. Tsavorite is not enhanced.

Tumbled stones were finished in a tumbler, a mechanical device that smoothes and rounds the surfaces of stones. Tumbled stones look very much like stones that have been in a fast-flowing river or stream for a long time.

A tumbler is a rotating cylinder (powered by a motor) that smooths and rounds the surfaces of stones, increasing their luster. As the stones tumble around the cylinder, they bump against each other and smooth each other’s surfaces.

Turquoise is a non-translucent, porous semi-precious stone that is usually cut as a cabochon. Turquoise was first found in Turkey, hence its name. Turquoise is found in desert regions worldwide. Persian turquoise is robin’s egg blue and has no matrix (streaks of the mother stone from which they were found). North American turquoise is greener and has a matrix streaks. Over the years, oil from your skin is absorbed by the stone and it will change color slightly. Turquoise has a hardness of 6 and a specific gravity of 2.60-2.85.

Twinning is a common error in crystalization in which two crystals grow out of one another or next to one another, and their crystal lattice is oriented differently from one another (some twins are like a mirror image of each other). If the crystals have grown into one another, they are called penetrant twins (forming a cross-shape like Staurolite, a star-shape like Muscovite, and other unusual shapes). If the crystals are mirror images that grow next to one another, they are called contact twins (they are often likened to Siamese twins). Twinning can drastically change the outward symmetry of the mineral specimen, by either increasing or decreasing the symmetry (like with spinel). For example, twinning can make an orthorhombic crystal appear to be hexagonal (as in Aragonite).

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