Blue is the colour for December with birthstones including stones such as tanzanite, blue zircon and turquoise. However these days, blue topaz is the most popular choice as the birthstone for December due to its bright colour and affordability.
Gemmology Matters: Topaz is a silicate mineral with the composition Al2SiO4(F,OH)2. Topaz is found in a range of colours although it is commonly very pale or colourless – in ancient times, the name “topaz” was used to refer to any yellow stone. Although topaz has a good hardness of 8, it has perfect cleavage along one direction – it can be split with a single blow and should be protected from hard knocks. For this reason, it is not recommended to clean topaz in an ultrasonic cleaner. In nature, blue is among the rarest of colours for natural topaz, however, the use of irradiation treatment to create vivid blue colours has made it the most commonly used colour for topaz in jewellery today. Pale topaz which is enhanced to become blue is found in Brazil, Sri Lanka, Nigeria, and China. All commercially available blue topaz has been treated to enhance colour which ranges from Sky (light), Swiss (medium) to London Blue (dark) as seen from left to right in the photo below. Generally London Blue Topaz is more expensive as it requires more treatment to achieve the deeper colour. 
Photo at left shows topaz before and after irradiation treatment (photo from EBIS Iotron) – note the dramatic change in colour.
Mythology and Lore: Blue topaz is said to enhance communicative abilities, helping to more easily and clearly express oneself. Historically, topaz was thought to give protection from poison, disease and sorcery. Blue topaz is the zodiac stone for the sign of Sagittarius and the anniversary gemstone for the 4th, 19th or 23rd years of marriage.
Photo from Palagems.com Topaz Buying Guide
Alternatives in Blue: There are many blue gemstones available representing the colours of the heavens. Blue zircon is perhaps the closest match in colour but these days is less commonly used as irradiated blue topaz has become the blue gem of choice for affordable jewellery. Blue sapphire is more valuable but is generally more saturated in colour. Aquamarine is another popular choice in blue but is generally much paler in colour. Tanzanite is another popular blue gemstone although the colour often has purple hues as well and limited supply can make this gem expensive.
Links of Interest:
- ICGA Gem by Gem article on Topaz
- Mineral Miners Fact Sheet on Topaz
- Professional Jeweller article on Blue Topaz treatment
- University of Texas, Dept Geological Sciences:
- Gem Notes on Topaz
- In conclusion, blue topaz is an excellent gemstone for use in affordable jewellery. Consumers should be aware of the use of irradiation treatments to create colour and possible alternatives which might be a more natural choice.
Cheers for now from Aussie Sapphire
April 21, 2006 at 7:54 am
This is a nice article on Blue Topaz. It is a very popular gemstone in Las Vegas and I get to handle a lot of it.
November 12, 2006 at 1:29 pm
[...] Green and blue topaz are naturally very pale, the very bright colours often found in jewellery today are the result in irradiation treatment - Sky Blue, Swiss Blue and London Blue are names used by the gem trade to refer to the depth of color. See our Blue Topaz article for more information. Please note that surface colour coatings are becoming more common in Topaz – starting with the multi-colour version of Mystic Topaz, but now also used to create other colours such as pink. Gems treated in this way should be treated with care to avoid damaging the colour coating. These types of gems should be far cheaper than naturally coloured stones so be wary when purchasing brightly coloured Topaz and ask about enhancement treatments first. [...]
December 11, 2006 at 10:29 am
[...] The modern birthstone for December is Turquoise (traditional or alternative birthstones include blue topaz, zircon and tanzanite). The example at left shows a beautiful sky blue colour with a dramatic black diagonal slash – from Aztec Moon. [...]
December 11, 2006 at 11:03 am
[...] The modern birthstone for December is Turquoise (traditional or alternative birthstones include blue topaz, zircon and tanzanite). The example at left shows a beautiful sky blue colour with a dramatic black diagonal slash – from Aztec Moon. [...]
December 12, 2006 at 4:49 pm
[...] The modern birthstone for December is Turquoise (traditional or alternative birthstones include blue topaz, zircon and tanzanite). The example at left shows a beautiful sky blue colour with a dramatic black diagonal slash – from Aztec Moon. [...]
December 17, 2006 at 1:33 pm
[...] Green and blue topaz are naturally very pale, the very bright colours often found in jewellery today are the result in irradiation treatment - Sky Blue, Swiss Blue and London Blue are names used by the gem trade to refer to the depth of color. See our Blue Topaz article for more information. Please note that surface colour coatings are becoming more common in Topaz – starting with the multi-colour version of Mystic Topaz, but now also used to create other colours such as pink. Gems treated in this way should be treated with care to avoid damaging the colour coating. These types of gems should be far cheaper than naturally coloured stones so be wary when purchasing brightly coloured Topaz and ask about enhancement treatments first. [...]
July 25, 2007 at 3:50 pm
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January 27, 2008 at 5:54 am
[...] modern birthstone for December is Turquoise (traditional or alternative birthstones include blue topaz, zircon and tanzanite). The example at left shows a beautiful sky blue colour with a dramatic [...]
September 6, 2008 at 6:42 pm
[...] modern birthstone for December is Turquoise (traditional or alternative birthstones include blue topaz, zircon and tanzanite). The example at left shows a beautiful sky blue colour with a dramatic [...]
September 6, 2008 at 6:46 pm
[...] Blue and London Blue are names used by the gem trade to refer to the depth of color. See our Blue Topaz article for more information. Please note that surface colour coatings are becoming more common in Topaz – [...]
September 6, 2008 at 7:08 pm
[...] December – Blue Topaz [...]