December Birthstones

The three birthstones associated with December are Tanzanite,  Zircon, and Turquoise.

Tanzanite

 

Tanzanite the mineral zoisite is a violet-blue gemstone, it was discovered 1967 on the foothills of Mount Kilimanjaro in Tanzania (hence its name), East Africa. Initially not considered gem material until transparent gems with a rich blue to purple colour were discovered. A green coloured gem variety has also been found.

Tanzanite has been adopted as a December birthstone and shares its last-month-of-the-year membership with turquoise and zircon.

This lovely gem can cost over $2,000 per carat, currently, in the larger sizes and at least $200 per carat for up to one and under one carat cut gems.

One must be careful with this gem, for example, in a ring settings as it is not that hard, at 6.5 on the Moh’s scale it can therefore scratch easily. Best to keep it separate from other gemstones and jewellery. It is also brittle and can “chip” easily.

A recent newspaper article covered the conundrum well.  Quote:The colour is a sapphire blue with overtones of violet, which only emerges after treatment in a gemstone oven. Although there are many – myself included – who had never heard of tanzanite, it is now a popular stone for jewellery. It is relatively cheap, at least compared with the big four – diamond, emerald, ruby and sapphire. This is largely due to its natural softness, with a tendency to chip if dropped: Unquote.

Reports that supplies of tanzanite are dwindling are not true. The market has been saturated with stones from the start, with 2 million carats’ worth released in the first five years after discovery. Tanzanite appears regularly on TV shopping networks in the US, usually hyped as rare and exclusive and generally given extravagant prices. These stones are likely to be of the lower quality. Tanzanite has recently started to appear on the secondary market in Australia and results show there is demand for high-quality items, with values steadily – if not dramatically – rising.

The deep blue of the tanzanite is fantastic, and runs from ultramarine blue to light violet-blue. The most coveted colour is a blue surrounded by a delicate hint of purple, which has a particularly wonderful effect in sizes of over 10 carats. The natural developed colour of the tanzanite is typical: depending on the angle from which you look at it, the stone may appear blue, purple or brownish-yellow. Having said that, most raw crystals are somewhat spoiled by a brownish-yellow component, though it can be made to disappear by the cutter if he heats the stone carefully in an oven to approximately 500°. During the procedure he must pay careful attention to the moment at which the colour turns to blue. This burning is a method of treatment which is regarded as customary in the trade, but the raw stones must be as free of inclusions as possible, since otherwise fissures may occur. In fact working with tanzanite can sometimes give even the most experienced cutter a bit of a headache, the cleavage of this gemstone being very pronounced in one direction. This exclusive gemstone is cut in every imaginable shape from the classical round shape to a number of imaginative designer cuts.

Blue Zircon

ZIRCON – Zircon is regarded as the traditional birthstone for December.

The fiery, brilliance of zircon can rival any gemstone. Zircon is one of the heaviest gemstones, which means that it will weigh more than other stones with the same measurements.
Natural zircon today suffers on account of the similarity of its name to “cubic zirconia”, the laboratory-grown diamond imitation, which is NOT zircon! Many people are unaware that there is a beautiful natural gemstone called zircon.
The wide variety of colours of zircon, its rarity, beauty, and its affordability make it a popular collector’s stone and contributes to its growing popularity among jewellery designers and gem lovers.

is not a very well-known gemstone, but it is one of the most important gemstones of today. Many people confuse zircon with the artificial diamond simulant, cubic zirconia. Of course, the two are completely different – cubic zirconia (CZ), is a lab-created synthetic material, while zircon is a naturally occurring gemstone with a very different chemical composition. However, before the introduction of diamond simulants like cubic zirconia and moissanite, white zircon was actually one of the most popular diamond substitutes, owing to its high dispersion and refractive index, and was often marketed under the misleading trade name of ‘Matura diamond’. Zircon is also remarkably dense and exhibits a very pronounced level of birefringence. Zircon has such high birefringence that it may appear fuzzy or display facet-doubling.

Zircon occurs in a wide range of colours, of which white or colourless is likely the least valuable or important. The most popular zircon today is blue zircon, usually occurring with green pleochroism, which can result in interesting teal-like colours. Blue zircon is actually produced by heating more commonly occurring brown zircon. However, only some brown materials have the appropriate physical structure to turn blue when heated, typically only deposits found in South East Asia – which is why most blue zircon comes from Cambodia or Burma. Blue zircon is one of the traditional modern birthstones for December.

Zircon is a tremendously important mineral, indeed its prominence led to the emergence of the discipline of zirconology in gemology. It is the oldest mineral on Earth, with samples found in Australia that are over 4.4 billion years old. Scientists discovered that zircon actually contains trace elements of uranium and thorium, both of which are elements with known half-lives. It is the uranium and thorium that cause such tremendous variations in the physical properties of zircon. Zircon is typically classified as low, medium and high zircon, in reference to the presence of optical properties. Low zircon has higher traces of radioactive uranium and thorium, which causes an alteration in physical structure, rendering it near-amorphous, though its physical appearance remains the same as high or medium zircon. Low zircon is typically green to brownish in colour. Green zircon is rarely seen in the gem trade and is highly sought after.

Zircon in its purest form is completely colourless (white), but owing to trace impurities, it can occur in a wide range of interesting colours, including yellow, orange, red, green, blue, violet, brown and combinations in between. Yellow-brown to orange and red zircon are the most common occurrences, along with colourless. Blue is the most popular, but its colour is obtained through the heating of brown zircon, usually from Cambodia and Burma. Due to pleochroism, blue zircon can look greenish from certain angles. Medium dark, pure blue stones have the most value. Green zircon is very rare and typically very expensive.