December Birthstone: Blue Topaz, Tanzanite & Turquoise Complete Guide (2026)

December is the only month with three official birthstones — and all three are blue. Tanzanite brings an extraordinary blue-violet color found nowhere else on Earth. Blue topaz offers brilliant, affordable blue in three distinct shades. Turquoise connects December birthdays to one of the oldest gemstone traditions in human history. Whether you're shopping for a December birthday or learning about these remarkable stones, this guide covers each in full — from the physics of tanzanite's trichroism to why "blue topaz is radioactive" is a persistent myth that needs to be put to rest.

At AJLuxe, our birthstone necklaces use genuine semi-precious stones set in 925 sterling silver — not glass or synthetic substitutes.

What Are December's Birthstones?

December's three birthstones were officially recognized at different points in history. Turquoise is the oldest — it has been worn as a gemstone for at least 3,000 years and appears on the jewelry of ancient Egyptians, Aztecs, and Native American cultures. Blue topaz replaced an older alternative (blue zircon) on the modern list and became widely popular after reliable irradiation treatments were developed in the 1970s. Tanzanite, the newest of the three, was added to the official birthstone list by the American Gem Trade Association in October 2002 — the first addition to the list since 1912.

Tanzanite — Earth's Rarest Blue

What Is Tanzanite?

Tanzanite is a blue-violet variety of the mineral zoisite, and it exists in commercial quantities in exactly one place on Earth: a roughly 7-kilometer strip of land in the Merelani Hills at the foot of Mount Kilimanjaro in northern Tanzania. This extreme geographic restriction makes tanzanite geologically unique among major gemstones — no other commercially significant gem is found in a single location of this size.

Geologists believe tanzanite required a very specific combination of events to form: tectonic plate collision (creating the East African Rift), extreme heat from nearby volcanic activity, and the presence of vanadium at exactly the right concentration. The probability of all these conditions occurring together in another location is estimated at roughly one million to one.

The estimated reserve of tanzanite ore is expected to last 20–30 more years at current mining rates. After that, no new tanzanite will enter the market. This finite supply is part of what drives tanzanite's growing reputation as an investment-grade gemstone — a stone that is "rarer than diamonds" in terms of its geographic restriction, a claim that holds up to geological scrutiny even if tanzanite's total market volume is currently smaller.

The Discovery of Tanzanite

Tanzanite was discovered in 1967. The most popular version of the discovery story involves a Maasai tribesman named Ali Juuyawatu who found unusual blue crystals after a lightning strike had started a grass fire in the Merelani Hills. He showed them to a prospector named Manuel de Souza, who initially thought they were sapphires. They were something entirely new.

Henry Platt of Tiffany & Co. recognized the stone's commercial potential and gave it its name — "tanzanite" — after Tanzania, its only source. Tiffany launched it with a major marketing campaign in 1968, calling it "the most beautiful blue stone discovered in 2,000 years." It went from obscurity to one of the world's most sought-after gemstones within a decade.

Tanzanite's Trichroism — Three Colors in One Stone

One of tanzanite's most scientifically fascinating properties is its trichroism — it shows three distinctly different colors when viewed from three different crystal axes:

• Blue — viewed along the c-axis (the main viewing direction in most faceted stones)
• Violet to purple — viewed along the b-axis
• Burgundy to red-brown — viewed along the a-axis

In practice, when you look at a finished tanzanite gemstone, you see a mixture of these colors — typically a blue-violet that shifts toward more blue in daylight (which has more blue wavelengths) and more violet in incandescent light (which has more red wavelengths). This color shift is part of tanzanite's appeal: the same stone looks slightly different depending on the lighting environment.

Raw tanzanite crystals are actually brown-reddish when first mined — the blue-violet color emerges only after heat treatment at around 600°C, which converts the mineral's vanadium oxidation state from V³⁺ to V⁴⁺. Nearly 100% of commercial tanzanite has been heat-treated; this is standard and fully accepted in the gem trade.

Blue Topaz — Beautiful, Affordable, and Brilliantly Clear

What Is Blue Topaz?

Topaz is an aluminum silicate fluoride mineral with excellent hardness (Mohs 8 — harder than quartz, garnet, or tanzanite). In its natural state, topaz is usually colorless, pale yellow, or pale pink. Natural blue topaz exists but is quite rare in gem quality. The vivid blue topaz found in virtually all jewelry today is produced by a reliable, well-understood process: irradiation followed by heat treatment.

Colorless topaz is first bombarded with neutrons (in a nuclear reactor) or electrons (in a linear accelerator), which changes the oxidation state of trace iron impurities and shifts the color toward blue or brown. A subsequent heat treatment removes the brown component and stabilizes the blue. The resulting color is permanent and stable — it does not fade with light exposure or time.

"Is Blue Topaz Radioactive?" — The Important FAQ

This is one of the most common questions about blue topaz, and the answer is important: finished blue topaz jewelry is not radioactive and is completely safe to wear.

Here's the full picture: immediately after irradiation, treated topaz does have residual radioactivity that exceeds safe handling limits. This is why treated topaz is held in licensed facilities and monitored with Geiger counters before release. By the time it reaches a jewelry store — typically 6–24 months after treatment — all radioactivity has decayed to levels far below natural background radiation. The Nuclear Regulatory Commission (NRC) and equivalent bodies in other countries set strict release standards. Only material that passes those standards enters the gem trade.

In short: the process uses radiation, but the finished gem does not contain radiation. It is as safe as any other gemstone.

Blue Topaz Varieties — Sky, Swiss, and London Blue

Blue topaz's combination of hardness (Mohs 8), clarity (naturally very few inclusions), excellent brilliance, and very low price makes it one of the best-value colored gemstones for everyday jewelry. A 5-carat Swiss Blue topaz of excellent quality might cost $50–$100 at the gem level — a fraction of what an aquamarine or sapphire of similar color would cost.

Turquoise — 3,000 Years of Human History

What Is Turquoise?

Turquoise is a hydrous copper aluminum phosphate mineral that forms when copper-rich groundwater reacts with aluminum and phosphorus in rock. Its distinctive blue-to-green color comes from copper (the blue component) and iron (which shifts it toward green). Pure turquoise with maximum copper and minimum iron is the most vivid sky blue; higher iron content produces greener stones.

Turquoise forms in arid regions where copper deposits are present — primarily in the southwestern United States, Iran, China, Egypt, and Mexico. It typically grows in veins and nodules within host rock; most turquoise is cut as cabochons that include some of the matrix (host rock), which creates the distinctive brown, black, or golden web-like pattern valued in many turquoise varieties.

Turquoise Through History

Turquoise is one of the first gemstones ever mined by humans. The Sinai Peninsula mines in Egypt were worked as early as 3200 BCE — over 5,000 years ago. Turquoise adorned the tombs of Egyptian pharaohs; the death mask of Tutankhamun is inlaid with turquoise. In Persia (Iran), turquoise was considered a national stone and used extensively in architecture, tile work, and jewelry. The famous blue dome of the Sheikh Lotfollah Mosque in Isfahan gets its color from turquoise-glazed tile.

In the Americas, Aztec rulers wore turquoise mosaic masks. The Navajo, Pueblo, and other Native American peoples of the Southwest have used turquoise in ceremonial and everyday jewelry for at least 1,000 years — it represents sky, water, and the connection between the physical and spiritual worlds in many Indigenous traditions.

In Persian folklore, turquoise was said to change color to warn of danger or illness approaching its wearer. This belief persisted in Europe through the medieval period, where turquoise was worn as a protective amulet.

Turquoise Quality and Varieties

The Sleeping Beauty mine closure: The Sleeping Beauty Turquoise Mine in Globe, Arizona was one of the most important sources of high-quality, matrix-free sky-blue turquoise in the world. It closed in 2012 when the mining company decided copper extraction was more profitable than gem mining. The closure significantly reduced the supply of clean American turquoise and has been driving up prices for existing Sleeping Beauty material ever since — a consideration for anyone purchasing high-quality American turquoise today.

Turquoise stabilization and treatment: Most commercial turquoise has been stabilized — impregnated with resin or epoxy under pressure to harden the stone and improve its color. This is standard practice for lower-grade porous turquoise and is generally accepted in the trade if disclosed. "Natural" or "gem-grade" turquoise that requires no treatment is genuinely rare and more expensive. Always ask whether turquoise has been stabilized, dyed, or is a composite (reconstituted turquoise powder with binder).

December Birthstone Meaning and Symbolism

Tanzanite Meaning

Tanzanite is associated with transformation, spiritual awareness, and the merging of the heart and mind. Its trichroic nature — showing blue, violet, and burgundy — has made it a symbol of multi-dimensional awareness. In crystal healing traditions, tanzanite is connected to the third eye and crown chakras, and is said to support the transition through major life changes. Its geographic uniqueness (one place on Earth) gives it a quality of rare, precious discovery.

Blue Topaz Meaning

Blue topaz is associated with clarity, communication, and truth. In Hindu tradition, topaz was associated with Jupiter and believed to bring wisdom and prosperity. Medieval Europeans carried topaz as protection against enchantment and sudden death. In modern crystal tradition, blue topaz is linked to the throat chakra and is said to help clear communication, reduce anxiety, and align the mind with truth.

Turquoise Meaning

Turquoise is one of the most universally used protective stones across human cultures. It has been worn for protection in battle by Aztec warriors, Persian cavalry, and Native American hunters. It symbolizes friendship, protection, good fortune, and connection to the sky and water. As a December birthstone, turquoise carries the deepest historical meaning of the three — a stone that has traveled across every major civilization over five millennia.

For more on turquoise's complete history, healing properties, and cultural significance, see our full guide to turquoise meaning and symbolism.

What Color Is the December Birthstone?

All three December birthstones share a blue color family, but each expresses it differently:

• Tanzanite: Blue-violet — it never looks exactly like any other blue gemstone because of its violet secondary hue and color-shift behavior
• Blue Topaz: Pure, clean, transparent blue — from pale sky blue to deep midnight London blue
• Turquoise: Opaque sky blue to blue-green — the only opaque stone of the three, and the only one with a matte rather than glassy finish

If someone asks "what color is the December birthstone?" — the answer is blue, but the specific tone depends on which birthstone you choose. The classic December birthstone color is the rich, slightly violet-tinted blue of tanzanite, but blue topaz and turquoise are equally valid and may suit different tastes.

How to Choose December Birthstone Jewelry

Tanzanite buying tips:

• Evaluate in both daylight and incandescent light — the color should shift between blue and violet
• The best tanzanite looks equally beautiful in both lighting conditions (not too gray in one or too brown in another)
• For 1ct+ stones, a GIA or AGL certificate is recommended
• Tanzanite should be set in protective settings — it's somewhat softer (Mohs 6–7) and can chip with hard blows

Turquoise buying tips:

• Ask specifically: Natural? Stabilized? Dyed? Reconstituted (compressed powder)? These are vastly different in value
• Natural, untreated turquoise with good color is rare and more valuable
• Stabilized turquoise is fine for everyday jewelry — just know what you're buying
• Sleeping Beauty and Persian turquoise command premiums; Chinese turquoise with good color is a budget alternative

How to Care for December Birthstone Jewelry

Topaz cleavage warning: Despite its hardness (Mohs 8), topaz has perfect basal cleavage — it can cleave (split cleanly) if struck from the right direction. This means a hard knock to a ring setting can split a topaz cleanly in half. Store topaz jewelry separately and consider protected settings (bezel or halo) for rings.

Gifting December Birthstone Jewelry

Frequently Asked Questions About the December Birthstone

What is the December birthstone?
December has three birthstones: tanzanite, blue topaz, and turquoise. Tanzanite was the most recent addition (2002) and is the most prestigious. Blue topaz is the most affordable and widely available. Turquoise is the most ancient, with a history spanning over 5,000 years.

What color is the December birthstone?
All three December birthstones are blue — but each with its own character. Tanzanite is blue-violet and shifts in color depending on the light. Blue topaz is a pure, clean, transparent blue ranging from pale sky to deep navy. Turquoise is an opaque sky-blue to blue-green. The most commonly associated December birthstone color is the blue-violet of tanzanite.

Is tanzanite really rarer than diamonds?
In terms of geographic restriction, yes — tanzanite is found commercially in a single location (approximately 7 km² in Tanzania) while diamonds are found on multiple continents. Total tanzanite supply is estimated to last only 20–30 more years at current extraction rates. In terms of total carat weight produced annually, diamonds exceed tanzanite significantly, but diamonds come from dozens of mines worldwide. The "rarer than diamond" claim is geologically supported.

Is blue topaz safe to wear — isn't it radioactive?
Finished blue topaz jewelry is completely safe. While the irradiation treatment uses radiation to change the stone's color, the finished gem is held in licensed facilities until all residual radioactivity decays to well below natural background radiation levels. By the time it reaches a jewelry store, it is no more radioactive than granite or concrete. The Nuclear Regulatory Commission certifies each batch before release.

What is tanzanite trichroism?
Trichroism means tanzanite shows three different colors depending on the crystal axis you view it through: blue (c-axis), violet-purple (b-axis), and burgundy-red (a-axis). In practice, a finished tanzanite shows a mixture of these colors — usually a blue-violet that shifts more blue in daylight and more violet under incandescent light.

How do I know if my turquoise is real?
Real turquoise is natural mineral material. Be aware of: dyed howlite (a white mineral dyed to look like turquoise — the dye bleeds with a cotton swab and acetone), reconstituted turquoise (ground turquoise powder + plastic binder), and stabilized turquoise (real turquoise but impregnated with resin to harden it). A jeweler with a loupe can often distinguish these, and a gemological lab test is definitive. Natural, untreated turquoise should be disclosed as such and commands a premium.

What is the difference between sky blue, Swiss blue, and London blue topaz?
All three are irradiated/heat-treated blue topaz, but different treatment conditions produce different shades. Sky blue is the palest — soft, light, aquamarine-like. Swiss blue is a vivid, saturated medium blue — the most popular shade for jewelry. London blue is the darkest — deep navy blue with a slight greenish or grayish undertone.

Does turquoise change color over time?
Natural untreated turquoise can change color if exposed to sweat, oils, chemicals, perfume, sunlight, or heat. The copper in turquoise can react with these substances, sometimes turning the stone greener or darker. This is normal for natural turquoise and is part of its character. Stabilized turquoise is more resistant to color change because the pores are sealed with resin.

Is tanzanite a good investment?
Tanzanite has appreciated in value over time, and with the mine's estimated 20–30 year lifespan remaining, many gem investors consider fine tanzanite a sound long-term hold. Investment-grade stones are 1ct+ AAA quality, certified by a reputable lab (GIA or AGL), and stored with documentation of provenance. As with all gemstone investments, liquidity is a consideration — you need a buyer when you're ready to sell.

Can I wear tanzanite every day?
Tanzanite can be worn daily with care, but it's better suited to earrings, pendants, and brooches than rings. Its Mohs 6–7 hardness means it can be scratched by dust, keys, and other everyday abrasives. If worn as a ring, choose a bezel or protective setting. Remove before exercise, household cleaning, or activities that involve hard impact.

What metal works best with December birthstones?
Tanzanite looks most beautiful in yellow gold (which enhances the violet tones) or white gold/platinum (which maximizes the blue). Blue topaz looks stunning against both white and yellow metals. Turquoise has a historic association with sterling silver, especially in Southwestern and Native American jewelry traditions — silver is the classic metal for turquoise.

How old is turquoise as a gemstone?
The oldest known turquoise mines were worked in the Sinai Peninsula by ancient Egyptians as early as 3200 BCE — over 5,000 years ago. Turquoise beads and jewelry have been found in pre-Columbian Mexican tombs, ancient Persian graves, and Egyptian royal burials. It is one of the first gemstones in human history to be mined, shaped, and worn intentionally.

December 1–21 birthdays fall under Sagittarius. Read our Sagittarius birthstone guide to see how turquoise and tanzanite connect to the Archer's personality.

Final Thoughts — Choosing Your December Birthstone

December's three birthstones offer something for every taste and budget. Tanzanite is the choice for those who want something truly rare — a stone with a known endpoint, a single source, and a color found nowhere else in the mineral world. Blue topaz is the choice for those who want beautiful, clear, vivid blue at an accessible price. Turquoise is the choice for those who feel the pull of history — a stone that connects the wearer to five thousand years of human civilization and countless cultures who prized it before us.

All three are unmistakably December — all blue, all unique, all deserving of their place in one of the most compelling birthstone groupings of any month.

Browse our December birthstone necklaces in sterling silver — crafted to show the best of tanzanite, blue topaz, and turquoise.

For the complete history and meaning of turquoise, see our guide to turquoise meaning, properties, and symbolism.

For a deep dive into zircon's history as Earth's oldest mineral and its spiritual symbolism, read our complete Zircon Meaning guide.

Written by Vaishakhi Ajmera — founder of AJLuxe, specialists in personalized sterling silver jewelry. Last updated: May 2026. | Sources: GIA Tanzanite · GIA Topaz · American Gem Society