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Section: December

December — Tanzanite and Turquoise and Zircon

Tanzanite, turquoise and zircon — three very different materials

All three are occasional wear at best. Turquoise is porous and must never meet solvents or an ultrasonic tank.

3 pieces in this month, ordered by how often they can sensibly be worn — the most forgiving first.

Mineralogy

Tanzanite is blue zoisite, calcium aluminium silicate, found in one small area of northern Tanzania and nowhere else. Mohs 6 to 7 with one direction of perfect cleavage. Turquoise is a hydrated copper aluminium phosphate, Mohs 5 to 6 and porous. Zircon is zirconium silicate, Mohs 7.5, with a dispersion close to diamond's — and it is a natural mineral, entirely unrelated to cubic zirconia, which is a manufactured imitation.

What the trade does to it

Almost all tanzanite is heated to turn a brownish crystal blue; it is declared here. Most commercial turquoise is stabilised with resin so it can be cut and worn at all — declared here on the piece, along with what it means for cleaning. Blue zircon is heated.

Documented history

Tanzanite was identified in 1967 and added to the December birthstone list in 2002 — the most recent addition to the modern list. Turquoise has been mined in Sinai and in the American Southwest for several thousand years.

December pieces

From £115 · all prices include VAT

Nothing in December reaches Mohs 8, so no piece in this month is graded for daily wear. If the piece needs to be worn every day without special care, look at April, July or September instead. We would rather say that than sell you something that will not survive the way you intend to wear it.

Wear grades in this month

  • Suitable for daily wear

    0 pieces in December

    • Remove before contact sports and heavy manual work
    • Remove before swimming pools and hot tubs — chlorine attacks the metal, not the stone

  • Occasional wear — avoid knocks

    2 pieces in December

    • Remove before gym equipment, gardening, DIY and washing up
    • Do not stack against harder stones, which will abrade this one
    • Avoid sudden temperature change

  • Delicate — special occasions only

    1 piece in December

    • Remove before any physical activity — knocks will chip this stone
    • Keep away from perfume, hairspray, cosmetics and hand sanitiser
    • Avoid sudden temperature change and prolonged dry heat
    • No ultrasonic tank, no steam, no soaking

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