December Birthstones

December has three official birthstones: turquoise, on the list since 1912, zircon, added in 1952, and tanzanite, added in 2002. All three are best known in shades of blue, from sky blue turquoise to the violet blue of tanzanite.

Tanzanite is the blue to violet variety of the mineral zoisite. It is mined commercially in only one place, the Merelani Hills near Mount Kilimanjaro in Tanzania, where it was discovered in 1967. It is strongly pleochroic, showing blue, violet and sometimes reddish tones depending on the viewing direction. Most tanzanite is heated to remove brownish tones, a standard practice in the trade.

Turquoise is an opaque copper aluminum phosphate valued for its sky blue to green color, often crossed by darker veins of its host rock, called matrix. It is relatively soft and porous, so many stones on the market are stabilized, and each listing states what applies.

Zircon is a natural zirconium silicate, not to be confused with synthetic cubic zirconia. It has a bright, almost diamond-like luster and strong fire, and some zircon crystals from Western Australia are about 4.4 billion years old, among the oldest known minerals on Earth. Blue zircon is usually produced by heating brownish stones.

Every stone here is natural, photographed individually and listed with its exact weight, dimensions and treatment status.

Month: December
Official birthstones: Turquoise, Zircon, Tanzanite
In this collection: Tanzanite, Turquoise, Zircon
Hardness (Mohs): Tanzanite 6 to 7, Turquoise 5 to 6, Zircon 6.5 to 7.5