December Birthstone: Tanzanite, Zircon & Turquoise
December is one of only three months assigned three modern birthstones: tanzanite, zircon, and turquoise. Each stone reached the December birthstone list at a different point in history — turquoise in 1912, zircon in 1952, and tanzanite in 2002. Of the three, turquoise has the deepest roots in antique jewellery, prized by Victorian jewellers for its vivid sky-blue colour and sentimental associations. This guide covers each December birthstone's history, properties, and place in the jewellery trade.
What Are the Three December Birthstones?
December's three birthstones are tanzanite, zircon, and turquoise. Turquoise has been mined for over five thousand years, zircon crystals are the oldest known terrestrial material at 4.4 billion years, and tanzanite was discovered only in 1967. Together they span an extraordinary range of geological age, colour, and cultural significance.
The concept of wearing a gemstone matching one's birth month traces to at least the first century and the writings of the historian Josephus. The three December stones arrived on the official birthstone list at different times. The American National Association of Jewelers established the first standardised list in August 1912, designating turquoise alongside lapis lazuli for December. In 1952, the Jewelry Industry Council of America replaced lapis lazuli with zircon. The American Gem Trade Association added tanzanite in 2002, making December one of the most gemstone-rich months on the calendar.
| Stone | Year Added | Hardness (Mohs) | Chemical Composition | Primary Source |
|---|---|---|---|---|
| Turquoise | 1912 | 5–6 | Hydrated copper aluminium phosphate | Iran, USA |
| Zircon | 1952 | 6–7.5 | Zirconium silicate | Cambodia, Sri Lanka |
| Tanzanite | 2002 | 6.5 | Calcium aluminium silicate (zoisite) | Tanzania |
Why Is Turquoise a December Birthstone?
Turquoise is the original December birthstone, appearing on the first standardised list in 1912. Mines near Nishapur in Iran have produced turquoise for over five thousand years, and Egyptian pharaohs sent expeditions to Sinai turquoise mines from the Early Dynastic Period, making it one of the earliest gemstones used in personal adornment.
Turquoise is a hydrated copper aluminium phosphate with a Mohs hardness of 5 to 6. Its blue colour comes from copper, while iron produces greener tones. Persian turquoise from Nishapur has long been considered the benchmark for quality — an intense, even sky blue with minimal matrix. The ancient Persians wore turquoise as protection against misfortune, and the stone was routinely attached to horse bridles to guard both rider and animal from falls. In Victorian England, turquoise became the stone of the forget-me-not flower, symbolising remembrance and enduring friendship. Across many cultures, turquoise has primarily represented hope — its colour connecting the stone to the sky.
How Was Turquoise Used in Victorian Jewellery?
Victorian jewellers set turquoise cabochons in 18ct yellow gold, often combining them with rose-cut diamonds and seed pearls. The forget-me-not flower motif was the most popular design, with turquoise cabochons arranged in petal formations around a central diamond, serving as tokens of love and remembrance.
Five-stone turquoise rings — with graduated cabochons separated by rose-cut diamond spacers — represent the classic Victorian format, produced primarily between 1860 and 1900. Cluster designs placed a central old-cut diamond surrounded by turquoise cabochons, while novelty pieces used pavé turquoise to form the bodies of serpents, flies, and doves. Queen Victoria favoured turquoise; upon her marriage to Prince Albert, she gifted portrait miniature rings surrounded by turquoise cabochons to her ladies-in-waiting. The stone's association with fidelity made it a popular engagement token across all social classes. The V&A Museum holds notable turquoise pieces in the Londonderry Collection, including stones purchased in Vienna in 1820. Browse our collection of antique turquoise rings to see examples spanning the Victorian era through the early twentieth century.
What Is Zircon and How Does It Differ from Cubic Zirconia?
Zircon is a naturally occurring zirconium silicate mineral — entirely unrelated to cubic zirconia, a synthetic zirconium dioxide manufactured commercially from 1976. Prized as a gemstone since at least the medieval period, natural zircon has a high refractive index, strong dispersion, and a distinctive doubling effect visible through the table facet.
Zircon crystals from Jack Hills in Western Australia are the oldest known terrestrial material, dated at 4.375 billion years by atom-probe tomography in a 2014 study published in Nature Geoscience. As a gemstone, zircon occurs in blue, colourless, golden, and green varieties. Blue zircon — produced by heat treating brown or reddish-brown stones, a process first reliably documented in 1927 — remains the most popular colour for December birthstone jewellery. Colourless zircon served as a diamond substitute in Georgian and Victorian rings, known in the trade as "Matura diamond" after the city in Sri Lanka near which many stones were sourced. With a Mohs hardness of 6 to 7.5 and dispersion of 0.039 (close to diamond's 0.044), zircon displays a fire and brilliance that few coloured gemstones can match. Its strong birefringence produces a visible doubling of back facet edges under magnification, a diagnostic feature that distinguishes zircon from diamond at a glance.
What Makes Tanzanite Unique Among December Birthstones?
Tanzanite is the newest December birthstone, added to the list in 2002. Found only in an area of approximately eight square kilometres near the Merelani Hills in Tanzania, it is often called a "one-generation gemstone" because no other deposit has been discovered anywhere in the world.
The stone was first identified in 1967 near Arusha, approximately 40 kilometres southeast of Mount Kilimanjaro. Manuel de Souza, a Goan prospector, found transparent blue and purple crystals at a ridge near Mererani and sent samples to the Gemological Institute of America for identification. Henry B. Platt, then vice president of Tiffany & Co. and great-great-grandson of founder Charles Lewis Tiffany, named the stone "tanzanite" in 1968, preferring it to the scientific name "blue zoisite". Tanzanite is a variety of the mineral zoisite, coloured blue-violet by trace vanadium. It ranks 6.5 on the Mohs scale and displays pronounced trichroism — appearing blue, violet, or burgundy depending on crystal orientation. Virtually all commercial tanzanite is heat treated at approximately 375°C to remove brown tones.
How Do December's Three Birthstones Compare?
The three December birthstones differ significantly in hardness, origin, and age. Zircon is the hardest and most brilliant of the three, turquoise the softest and most historically significant in antique jewellery, and tanzanite the rarest — sourced from a single deposit in East Africa.
| Property | Turquoise | Zircon | Tanzanite |
|---|---|---|---|
| Mohs hardness | 5–6 | 6–7.5 | 6.5 |
| Chemical composition | Hydrated copper aluminium phosphate | Zirconium silicate | Calcium aluminium silicate (zoisite) |
| Crystal system | Triclinic | Tetragonal | Orthorhombic |
| Typical colour | Sky blue to green | Blue, colourless, golden | Blue-violet |
| Transparency | Opaque | Transparent | Transparent |
| Key optical property | Waxy lustre | Birefringence (doubling effect) | Trichroism |
| Earliest known use | c. 4000 BC (Egypt) | Medieval period | 1967 |
Turquoise is a cryptocrystalline aggregate that never forms visible single crystals, distinguishing it structurally from zircon and tanzanite, which both produce transparent faceted gemstones. Zircon's high refractive index of 1.925 to 1.984 and dispersion close to diamond make it the most optically striking of the three. Tanzanite's appeal lies in its colour — a saturated blue-violet that shifts hue under different lighting conditions. Explore our gemstone ring collection to see December birthstones and other precious stones in antique settings. Visit the A-Z of Gemstones reference page for detailed profiles of these and other gemstones found in antique jewellery.
How Should You Care for December Birthstone Jewellery?
Care requirements vary across December's three birthstones because their hardness and porosity differ substantially. Turquoise demands the most caution at 5 to 6 on the Mohs scale and is porous enough to absorb damaging substances. Zircon and tanzanite are moderately hard but still softer than sapphire or diamond.
| Turquoise | Zircon | Tanzanite | |
|---|---|---|---|
| Cleaning method | Warm soapy water only | Warm soapy water | Warm soapy water |
| Ultrasonic/steam | Never | Avoid | Never |
| Main risk | Colour change from oil absorption | Chipping along facet edges | Cleavage cracking from impact |
| Daily wear | Occasional wear only | Suitable with care | Protective setting advised |
Turquoise absorbs oils, perfumes, and cosmetics through its surface, permanently altering its colour over decades of wear. Many antique pieces contain untreated natural turquoise, rarer and more valuable than modern stabilised material but also more susceptible to environmental damage. Zircon, despite its higher hardness, has a brittle crystal structure that can chip along facet edges; store zircon rings separately and avoid sharp impacts. Tanzanite's perfect prismatic cleavage makes it vulnerable to knocks, and it suits earrings and pendants better than daily-wear rings. For all three stones, remove jewellery before applying perfume or household cleaning products.
Frequently Asked Questions
Which December birthstone is the most valuable?
Tanzanite commands the highest prices per carat among the three December birthstones. Fine quality tanzanite in deep blue-violet can exceed the per-carat price of sapphire at comparable sizes. Turquoise values vary enormously depending on treatment and origin — untreated Persian turquoise with even colour and no matrix is the most prized. Natural zircon, while undervalued due to name confusion with cubic zirconia, represents strong value for collectors seeking high brilliance at accessible prices.
Can turquoise change colour over time?
Turquoise can and does change colour with age. Its porous structure absorbs oils from skin contact, cosmetics, soaps, and airborne pollutants, and over decades of wear an originally sky-blue stone may shift towards green. This colour change is permanent in untreated turquoise. Antique turquoise that retains its vivid original blue is exceptionally desirable, as it indicates either superior stone density or careful storage over the intervening years.
Is zircon the same as cubic zirconia?
Zircon and cubic zirconia are entirely different materials. Zircon is a naturally occurring mineral — zirconium silicate — found in the Earth's crust for billions of years. Cubic zirconia is a synthetic material — zirconium dioxide — first commercially produced in the USSR in 1976. The similar names have damaged zircon's reputation among consumers, but the two share no chemical or structural relationship.
Where is tanzanite found?
Tanzanite is found exclusively at the Merelani Hills in the Simanjiro District of Tanzania's Manyara Region. The mining area covers approximately eight square kilometres. No other deposit has been identified anywhere in the world. The stone formed 585 million years ago during regional metamorphism, with its blue-violet colour caused by vanadium originating from organically derived graphite within the host rock.
Which December birthstone is best for an engagement ring?
Zircon offers the best combination of hardness and brilliance for daily wear, with its 6 to 7.5 Mohs rating and diamond-like fire. Turquoise suits rings worn less frequently, as its softness and porosity require careful handling. Tanzanite's cleavage makes it better suited to protective bezel settings. For antique rings, turquoise dominates the December birthstone market. Browse our Victorian ring collection for turquoise examples from the era that favoured the stone most.
Related Reading
- Turquoise in Antique Jewellery — a full guide to turquoise history, properties, and use across the eras
- Gemstone Symbolism: What Stones Really Mean — the meanings behind precious and semi-precious stones in antique jewellery
- Victorian Rings: Romance, Mourning & Empire — the era that produced the finest turquoise jewellery in Britain
- Explore our complete guide to gemstones in antique rings — the Gemstones pillar page