December: Tanzanite, Zircon, Turquoise

Tanzanite: This gemstone is one of three representing December. It is the most precious variety of the mineral zoisite. Before its discovery in 1967, the only varieties of zoisite that had any pretensions as gem material were the pink ornamental mineral known as thulite, and the green chrome-rich material that acts as the matrix for the large hexagonal crystals of ruby found in Tanzania, which is called “ruby in zoisite”. The name zoisite comes from the name of its discoverer, the Austrian Baron Von Zoïs, who discovered it in 1967 in Tanzania, hence the name tanzanite.

Tanzanite is a transparent gemstone; its colour varies from blue to violet to bluish purple. These shades of blue take on a more purple tinge when viewed under incandescent light. The blue colour of tanzanite is rarely natural—it is generally a result of heat treatment.
The transparent crystals of zoisite are found in various colours: blue, green, yellow, pink, brown and khaki. These shades of colour turn to the favoured blue on careful heat treatment, and this is usually carried out. Thulite is translucent to opaque pink, often mottled or streaked with grey or white. Ruby in zoisite is translucent to opaque rock-like ornamental material with ruby crystals in green zoisite.

Tanzanite is not a tough gem; it is rather fragile. Its impact resistance is rated as medium to low. It discolours and melts under the heat of a jeweller’s blowtorch. What’s more, it fractures easily at high temperatures or when subjected to a sudden change in temperature.

Zircon: December is also the month of zircon. Zircons are transparent, but can be colourless, blue, yellow, green, brown, orange, red, and occasionally purple. Because of its vast range of colours, zircons may be confused with many gems, including diamond, topaz, aquamarine, demantoid and spessartine garnets, heliodor, green beryl and chrysoberyl.

Zircons are very resistant to acids and other chemicals. However, the colour heat- treated stones may revert to their original colour in daylight. Steamer and ultrasonic cleaners are not recommended for cleaning jewellery set with a zircon.

The most popular colour is a pastel blue, but some exceptional gems have a bright blue colour. Most zircons are heat treated to improve their colour particularly blue and golden. Blue zircons were widely used until the middle of the 20th century. Generally speaking, zircons are a vivid and attractive colour and are readily available and affordable.

Zircon jewellery should be stored carefully because although zircon is relatively hard, it can abrade and facets can chip. Dealers often wrap zircons individually so that they will not knock against each other in a parcel.

The main deposits are in Cambodia, Sri Lanka, Thailand, Myanmar and Australia.

Turquoise: The name turquoise, from the French expression Pierre tourques or Turkish stone, originated in the thirteenth century and describes one of the oldest known gemstones. Turquoise varies in colour from greenish blue, through robin’s egg-blue, to sky blue shades and its transparency ranges from translucent to opaque. Its shining sky blue is one of the most popular trend colours in the world of jewellery and fashion.

Throughout the world turquoise has been worn as natural protection against the powers of darkness. In earlier times this gemstone was used to protect horse and rider from unexpected falls. It is still considered a symbol of protection particularly for pilots, aircrews and other high-risk professions.

In modern gemstone therapy, those suffering from depression are recommended to wear a turquoise or a chain with turquoise beads. The cheerful colour of the turquoise is said to provide confidence to quiet and reserved individuals. It is also a stone of friendship, symbolizing faithfulness and constancy in relationships.

Turquoise is plentiful and available in a wide range of sizes. This gemstone is also allocated to December.

* image courtesy the American Gem Trade Association (AGTA)