December has three birthstones – zircon, tanzanite and turquoise. The 1912 list of birthstones developed by the American National Jewellers Association had turquoise as the main gemstone for December with lapis lazuli, another opaque blue stone, as the alternate. In 1952, zircon was added to the list and lapis lzuli disappeared. In 2002, tanzanite was added. The National Association of Goldsmiths list of birthstones in 1937 had turquoise. It later added tanzanite as well, but not zircons. Sometimes, blue topaz is added in the UK as a December stone.
So let’s talk about turquoise, the main December gemstone. It has a long history of use as a gemstone, popular with the Egyptians, Romans and Aztecs. The name ‘turquoise’ arose in the 17th century, derived from the French expression ‘pierre tourques’ (Turkish stone) as it was believed to have been mined in Turkey. It actually came from Persia (now Iran) where it was mined for over 2000 years.
Turquoise has been imitated a lot over the centuries and antique jewellers used glass, faience, mammoth ivory and glass. It is hard to detect imitation turquoise. However, because turquoise is very porous and can darken and turn greener due to perspiration and access to water, discolouration of turquoise beads is often a good sign in antique jewellery as is is a strong indicator that the turquoise is real and not glass or dyed ivory.
Zircons are beautiful gemstones. Because they are highly refractive, they reflect a lot of light and and so show sparkles and fire. They range in colour from shades of of brown, yellow, blue, green and colourless (white). The gem is heat treated, particularly to produce intense blue colours, but for other colours as well.
Zircon has been used in jewellery for 1000s of years under various names, such as jargoon, and hyacinth or jacinth. Pliny is thought to have called it chrysolithos, describing it as a yellow stone. The name ‘zircon’ was derived from either Arabic or Persian words around 1783.
Tanzanite is a member of the Zoisite family of minerals and a deposit was only discovered gemstones in Tanzania in 1967. Tiffany’s bought the rights to sole distribution and Henry B Platt, Tiffany’s Chair at the time, named the new gemstone ‘Tanzanite’. The firm promoted the stone extensively and managed to get it accepted as the third gemstone for December. Good quality tanzanite can be a deep blue, with a touch of lilac or purple. It is heat treated but a lovely stone.