The December birthstone is generally known as blue Zircon or Turquoise.  I can relate to blue Zircon being the birthstone for December since the color is similar to the purest glacier-ice blue.  Turquoise is also a traditional choice for December and is considered a talisman for successfulness.  Your choices don’t end there however.  There are lots of gems that have become accepted alternatives.

Swiss Topaz and lab blue Spinel have extremely similar colors to the blue Zircon and therefore are great lower cost alternatives.  The lab blue Spinel is so close in color and optical properties that in many cases it is nearly impossible to tell which is which with the eye.  A refractive index test will resolve the confusion quickly.

Tanzanite has squeezed itself into the mix somehow.  The color is way more purple and has only been accepted as a December birthstone for a decade.  Personally, getting Tanzanite accepted as a December birthstone is just another demonstration of what this generation of money and advertising can buy.  I recommend you own a Tanzanite just because it is a beautiful, valuable and rare gem.

Lapis Lazuli is a weak alternative to Turquoise, but also considered a December alternative.  Since Lapis is often more expensive, there’s not much motivation for buyers to divert from the traditional Turquoise.  For us in the United States, we tend to prefer Turquoise since it is one of the few birthstones that is predominantly found in the U.S.  Arizona is now one of the largest producers of Turquoise in the world.