December Birthstone: Blue Zircon, Tanzanite & Turquoise Jewelry

December has three in the modern list: turquoise, blue zircon and tanzanite. Any of them is correct for a December birthday.

They are strikingly different from one another. Tanzanite is a transparent violet-blue, blue zircon is brilliant and fiery, and turquoise is opaque and matte.

Tanzanite is the newest addition, added in 2002, and turquoise the oldest association by thousands of years.

No, and the similarity of the names is unfortunate because the two have nothing to do with one another.

Zircon is a natural mineral - zirconium silicate - used in jewellery for thousands of years, and among the oldest minerals found on earth.

Cubic zirconia is a man-made material developed in the twentieth century as a diamond simulant. Where a listing here says blue zircon, it means the natural mineral.

A single small area of northern Tanzania, near Mount Kilimanjaro. It is not found anywhere else on earth, which is genuinely unusual for a commercially significant gemstone.

It was identified in 1967, which makes it the newest stone on the birthstone list by a wide margin - it was added to December only in 2002.

That single source is a large part of why the stone attracts the attention it does.

It needs thought. Tanzanite sits around 6 to 7 on the Mohs scale and has a distinct cleavage direction, which makes it more vulnerable than that number alone suggests.

It is also sensitive to sudden temperature change. For a ring worn every day, that is a real consideration, and a bezel setting with a lower profile helps considerably.

As a pendant or in earrings, tanzanite is entirely practical - and in a ring worn for occasions rather than constantly it is a perfectly reasonable choice.

Because it is opaque. Faceting works by returning light that has entered the stone, and light does not travel through turquoise the way it does through a transparent gem.

A cabochon - a smooth polished dome - shows turquoise's colour and its matrix veining to best effect, which is what the stone is admired for.

This is the same reason opal, moonstone and other stones prized for surface effect or colour rather than refraction are typically cut as cabochons.

Matrix is the veining of surrounding host rock that runs through a turquoise stone, appearing as brown, black or golden lines and webs across the blue.

Whether it is desirable is genuinely a matter of taste and tradition. Some buyers prize clean, unmarked blue; others specifically seek out a dramatic spiderweb matrix.

Neither preference is more correct. It is one of the few places in gemstones where the 'flaw' is often the reason someone chooses a particular piece.

Much commercial turquoise is stabilised, which means a clear resin is introduced to harden the stone and make its colour more stable.

This is standard practice and openly disclosed. It exists because natural turquoise is soft and porous enough that untreated material can change colour with wear.

Stabilised turquoise is still turquoise - the treatment reinforces the stone rather than replacing it. Untreated material of good colour is uncommon and priced accordingly.

More carefully than any other stone in this collection. Turquoise is soft, around 5 to 6 on the Mohs scale, and genuinely porous.

It absorbs liquids, oils and chemicals. Perfume, lotion, cleaning products and even body oils can alter its colour permanently with prolonged contact. Put jewellery on after those have dried, and take it off before swimming or cleaning.

Clean it with a dry or barely damp soft cloth only. Never soak it, and never use an ultrasonic or steam cleaner.

None of the three is a hard stone, which is worth knowing up front. Blue zircon at roughly 6 to 7.5 is generally the most robust of them, though its facet edges can abrade over time.

Tanzanite at 6 to 7 has a cleavage direction that makes it more fragile than the number suggests. Turquoise at 5 to 6 is the softest and also porous.

All three suit pendants and earrings very well. For a ring worn daily, a protective bezel setting and a degree of care make a real difference with any of them.

White gold and platinum give tanzanite and blue zircon a cool, clean background that lets their blue read clearly, and they are the most common pairing for both.

Yellow gold is the traditional setting for turquoise and has a long history in the southwestern American and Persian traditions - the warm metal against the opaque blue is a recognisable combination.

Rose gold works as a deliberate contrast with all three. Since these stones differ so much from one another, it is worth judging each design on its own rather than applying a rule.