The Tanzanite
Laid Bare

What Is the December Birthstone?

December has three birthstones: tanzanite, zircon, and turquoise. Tanzanite is the most recent addition, added to the official list in 2002 by the American Gem Trade Association. It was the first change to the birthstone list since 1912. Tanzanite is a variety of the mineral zoisite, found in a single location on Earth: the Merelani Hills in northern Tanzania, roughly 90 kilometers southeast of Arusha, in the shadow of Mount Kilimanjaro.

The mining area is approximately 4.3 miles long and 1.2 miles wide. That's roughly twice the footprint of Central Park in New York. There is no other known deposit of gem-quality tanzanite anywhere on the planet. Geologists estimate the likelihood of finding another deposit at one in a million, making tanzanite roughly 1,000 times rarer than diamond.

Tanzanite is trichroic: it displays three different colors from three different viewing angles. In its natural state, those colors are blue, violet, and burgundy. Heat treatment (370–390°C) removes the brownish component, leaving a dichroic stone that shifts between violet-blue and blue-violet. Almost all commercial tanzanite is heat-treated. The treatment is permanent and stable. At 6 to 6.5 on the Mohs scale, tanzanite is softer than most colored gemstones and requires careful handling.

Tanzanite Meaning & Symbolism

The Gemstone of a Generation

Tanzanite has been called "the gemstone of a generation" because this generation may be the last able to buy stones from the primary market before the supply runs out. That's not marketing language. It's geology. The mines are finite, the deposit is singular, and production is declining. Every tanzanite sold today carries the weight of genuine scarcity.

The Maasai people of Tanzania have their own origin story: a bolt of lightning struck the foothills of Kilimanjaro, setting the grasslands ablaze. When the fires cooled, the brown zoisite crystals in the earth had been transformed into shimmering blue-violet gems. The Maasai traditionally give blue beads to mothers of newborn children, a blessing for health and a positive life. The Tanzanite Foundation has proposed extending that tradition to Western cultures, positioning tanzanite as "the gem of birth."

The 24th Wedding Anniversary Stone

Tanzanite is the gemstone for the 24th wedding anniversary. Given that it may not be commercially available forever, a tanzanite anniversary piece is increasingly a gift that comes with a built-in timeline.

The Discovery of Tanzanite

In January 1967, Manuel de Souza, a Goan tailor and part-time gold prospector living in Arusha, found fragments of transparent blue-violet crystals on a ridge near the Merelani Hills. He initially thought they were peridot. When testing proved otherwise, he concluded they were dumortierite. They were neither.

The stones reached John Saul, a Nairobi-based geologist, who sent samples to his father Hyman Saul, a vice president at Saks Fifth Avenue in New York. Hyman took them across the street to the Gemological Institute of America, who identified them as a previously unknown gem variety of the mineral zoisite. The scientific name "blue zoisite" was correct but sounded uncomfortably close to "blue suicide." Henry B. Platt, great-grandson of Louis Comfort Tiffany and a vice president of Tiffany & Co., renamed it "tanzanite" and launched a campaign declaring it could be found "in two places: in Tanzania and at Tiffany's."

An estimated two million carats were mined before the Tanzanian government nationalized the mines in 1971. Today, the government has built a security wall around the entire mining area with a single military checkpoint for entry and exit. The mines are divided into four blocks (A through D), with only Block C still commercially producing rough tanzanite at meaningful scale.

December's Second Stone: Zircon

4.4 Billion Years Old. Not Cubic Zirconia.

First: zircon is not cubic zirconia (CZ). They are completely unrelated. The name confusion has been disastrous for zircon's reputation. Zircon is a natural mineral (zirconium silicate) and one of the oldest materials on Earth. Zircon crystals from the Jack Hills of Western Australia have been dated to 4.4 billion years old, predating the formation of the Earth's crust and making them the oldest known terrestrial materials.

Blue zircon is the traditional December birthstone and one of the most brilliant natural gemstones. Zircon has a refractive index close to diamond and displays strong fire (dispersion). Look closely at a well-cut zircon and you'll notice doubled facet edges: an effect of its double refraction that creates a distinctive, almost fuzzy sparkle that diamond doesn't have. It's how gemologists spot zircon immediately.

Blue zircon is almost always heat-treated from brownish or reddish material. The name may come from the Persian zargun (gold-colored) or the Arabic zarqun (vermillion). At 6 to 7.5 Mohs, zircon is moderately hard but can be brittle at the edges of facets. Cambodia, Sri Lanka, and Myanmar are the primary sources. In the Middle Ages, zircon was believed to aid sleep and bring prosperity.

December's Third Stone: Turquoise

7,000 Years of Sacred Blue

Turquoise is one of the oldest gemstones in human history. It has been mined, carved, and worn for over 7,000 years. The name comes from the French pierre turquoise, meaning "Turkish stone," because it first reached Europe through Turkish trade routes. Turquoise itself is a copper aluminum phosphate, and the copper is what gives it that iconic robin's-egg blue.

Egyptian pharaohs wore turquoise. King Tutankhamun's burial mask is inlaid with it. The Sinai Peninsula mines that produced those stones have been dated to 6,000 BCE, making them among the oldest known mines in the world. Turquoise is sacred to Native American cultures, especially the Navajo, Zuni, and Pueblo peoples, who incorporated it into jewelry, ceremony, and daily life for centuries. The squash blossom necklace, one of the most iconic pieces of Native American jewelry, centers on turquoise.

Iran's Nishapur mines produce the finest turquoise on Earth: an intense, even blue without visible matrix (veining). Persian tradition holds that turquoise seen under the first moon of the new year brings good luck. At 5 to 6 Mohs, turquoise is soft and porous. Most commercial turquoise is stabilized (impregnated with resin) to improve durability and color permanence. The finest untreated material from Iran commands premium prices.