The Blue Topaz, Turquoise or Tanzanite are the Birthstones for December. 

The topaz gemstone is a hard gemstone. The topaz comes in the colours of yellow, pink and blue.  The topaz hardness is 8.0.  The Turquoise gemstone is porous.  Turquoise is light blue to bluegreen in colour.  Turquoise hardness is 5.0.-6.0.  The Tanzanite gemstone discovered in Tanzania was originally brown and only with heat does it show its true blue colour.  When viewed in different directions it shows different colours, one blue, one purple and one bronze.  Tanzanite hardness is 6.5.

Topaz is said to reduce mood swings and worries.  The wearer of topaz wears the gemstone to be clear-sighted.  Turquoise is considered a general healer, the gift of a turquoise rings means "forget me not" in European tradition.  Tanzanite is used to uplift and open the heart.

Blue Topaz is also the 23rd anniversary gemstone. 

Turquoise is also the 11th anniversary gemstone. 

Tanzanite is also the 24th anniversary gemstone