The December birthstone tanzanite is the youngest gem on any birthstone list and the only one that comes from a single place on earth. It was identified in the 1960s in a few square miles of hills in northern Tanzania, and nothing comparable has been found anywhere else since. That scarcity, plus a violet blue that shifts as you turn it, explains why a stone nobody had heard of sixty years ago now sits alongside turquoise and zircon as a December birthstone. Here is what tanzanite is, what it has come to mean, and how to choose a December gift around it.

What tanzanite is, and why there is only one source

Tanzanite is the blue violet variety of a mineral called zoisite, colored by traces of vanadium. Zoisite itself is common and mostly unremarkable. The combination of geological conditions that produced gem quality blue zoisite appears to have occurred in one small area at the foot of Kilimanjaro, in the Merelani Hills, and prospecting elsewhere has not turned up a second deposit.

It was identified as a new gem in the late 1960s, and the name came from the jewelry trade rather than from geology: Tiffany and Company, which brought it to a wide market, named it after the country it came from. That is unusual and worth knowing, because it means tanzanite's fame and its supply are tied to the same few decades.

The most striking optical property is trichroism. Depending on the angle you view it from, a single tanzanite crystal can show blue, violet and a brownish burgundy. Cutters orient the rough to favor blue or violet, and the choice changes both the look and the price.

Almost all tanzanite is heat treated. Most rough comes out of the ground a muddy brown, and gentle heating produces the blue violet the stone is known for. The treatment is stable, universal and disclosed; untreated blue material exists but is rare.

Hardness is around 6 to 7 on the Mohs scale, and the crystal has cleavage, so it is more delicate than its price suggests.

What the December birthstone tanzanite symbolizes

Because tanzanite is new, it has no ancient folklore, and anyone who tells you otherwise is inventing tradition. What it has instead is a set of modern associations that grew up around the story of its discovery: transformation, new beginnings and rarity.

Transformation is the most literal of these. The stone arrives brown and becomes blue; the change is part of its nature rather than a flaw concealed. For someone who has come through a period of change, or who is in the middle of one, that is a genuinely apt gift with an honest story behind it.

Rarity does the rest of the work. A single source, discovered within living memory and expected to be exhausted within a few decades, makes tanzanite a gem with a horizon. Gifts that carry a sense of finite time land differently from ones that do not.

For a December birthday, that suits the newest member of a family particularly well: a granddaughter, a first baby, a daughter in law joining a family with decades of its own history. The stone is the youngest thing on the list and it has already earned its place, which is a message worth putting into words.

Choosing a December birthstone tanzanite gift for the youngest in the family

December's crowding problem applies here too, so the same rule holds: birthday gift and holiday gift stay separate, with separate cards, ideally on separate days.

For a daughter

The Always My Baby Eternal Hope necklace works at almost any age, because the sentiment does not expire when a daughter turns thirty. Look through the full Eternal Hope collection if you want the same idea with different wording.

For a granddaughter

The Never Forget interlocking hearts necklace is written from a grandparent, which is a voice most jewelry never manages, and the Before You Could Even Stand interlocking hearts necklace is for the grandparent who was there from the first week. Both come with a printed card, and the wider range of gifts for a granddaughter covers several ages and tones.

If you want the stone itself

Choose a pendant or earrings rather than a ring. Tanzanite is beautiful and comparatively delicate, and a ring worn daily is the fastest way to chip one. Buy for the blue you actually like under normal indoor light, because trichroism means the stone in the case and the stone at home can look different.

What to write when the gift marks a new beginning

Cards about new beginnings usually address the future, and the future is the least interesting thing you can write about, because neither of you knows anything about it.

Write about the change already behind her instead. Name what she came through this year, briefly and without drama, and say what it showed you. Then stop. A single line about what comes next is enough, and it should be a promise about you rather than a prediction about her: that you will be there, that nothing changes.

For a granddaughter or a very young child, write the card to the adult she will become. Those cards get reread at fifteen and at thirty, and the version written for a five year old does not survive that. Say what you want her to know when she is old enough to want to know it.

Date it. An undated card loses half its meaning in twenty years, and the date costs you nothing.

Caring for tanzanite

Tanzanite is the most delicate of the December stones after turquoise, and the reason is cleavage rather than softness. It scores 6 to 7 on the Mohs scale, but the crystal can split along a plane if struck, so a sharp knock matters more than daily abrasion.

Never put tanzanite in an ultrasonic cleaner, and keep it away from steam and sudden temperature changes, which can crack it. Household chemicals should be avoided as well. Warm water, mild soap and a soft brush, used gently, are all it needs.

Take it off for sport, cleaning and anything involving impact, and put it on after perfume and hand cream rather than before. Prefer settings that protect the edges of the stone, such as a bezel, especially for a piece someone will wear often.

Store it on its own, cushioned, away from harder stones. Keep the printed card from a gift flat and dry in the same box so the words and the piece stay together. Our jewelry care tips cover chains, storage and the sturdier pieces in the same collection.

When to give it

The same December discipline applies: give the birthday gift on the birthday, keep the holiday gift for the holiday, and do not wrap either in the other's paper.

If the gift marks a beginning rather than a date, the beginning is the better occasion. The week a baby comes home. The day a young woman moves into her first place. The evening before a wedding. Tanzanite's story is about change, and a gift given at the moment of change is doing what the stone is for.

Give it somewhere quiet enough that the card gets read properly. In December that usually means before the house fills up, or after it empties.

Questions buyers ask

Where does tanzanite come from?

A single small area in the Merelani Hills of northern Tanzania, near Kilimanjaro. No comparable deposit has been found anywhere else, which is why tanzanite is described as a one source gem and why supply has a foreseeable end.

Is tanzanite heat treated?

Almost always. Most rough is brownish when mined, and gentle heating brings out the blue violet color the stone is known for. The treatment is stable and standard across the trade. Untreated blue material exists but is uncommon.

Is tanzanite durable enough for daily wear?

It is better suited to pendants and earrings than to rings. At 6 to 7 on the Mohs scale with cleavage, it can chip or split from a sharp knock, so protect the edges with the setting and take it off for anything physical.

Why is such a new stone a December birthstone?

It was added to the standard list in 2002, decades after its discovery in the 1960s. Birthstone lists are revised occasionally by the jewelry trade rather than fixed by ancient tradition, which is also how spinel was added for August.