December has three stones on the modern list, turquoise, tanzanite and zircon, and two on the traditional list, tanzanite and turquoise.
The two lists for December
Modern list (American Gem Society): Turquoise, Tanzanite, Zircon
Traditional list (United Kingdom, National Association of Goldsmiths, 1937): Tanzanite, Turquoise
There is no single official birthstone list, so you are free to choose whichever you prefer. You can check any month with our birthstone finder.
About the stones
Turquoise
Turquoise is an opaque blue-green copper aluminium phosphate, hardness 5 to 6, worked into jewellery in Persia, Egypt and the Americas for thousands of years. It is porous, so it can be marked by oils and cosmetics. See the turquoise guide.
Tanzanite
Tanzanite is blue-violet zoisite, first described in 1967 and found only near Mount Kilimanjaro in Tanzania. Nearly all tanzanite is heated to bring out the blue. Its hardness is about 6.5 and it can be damaged by knocks.
Zircon
Zircon is a natural zirconium silicate found in many colours, including blue, with a hardness of 6.5 to 7.5. It is not cubic zirconia, which is a manufactured imitation. Some zircon crystals are among the oldest minerals ever found on Earth, dating back more than four billion years.
How the idea developed
December is the month in which the modern list has changed most in recent decades, with tanzanite being a twentieth-century discovery. A stone first described in 1967 has gone on to join a list that began with much older choices, which shows that birthstone lists are conventions that shift.
For the wider history of the idea, see our birthstones overview. The modern list follows the American Gem Society, and the traditional list follows the 1937 United Kingdom list, both summarised in Wikipedia, Birthstone.
A different system
Vedic gemstone (ratna) guidance is a different system from birthstones. It is tied to the nine planets and to a birth chart, not to the calendar month, and it belongs to the Vedic tradition, which is covered on our sister site, Nidarshana Vedh. Nothing on this page is Vedic advice.
A note on health. Crystals are valued for beauty, meaning and ritual. There is no scientific evidence that they treat health conditions. If you are struggling with your health or mood, please speak to a doctor.
Frequently asked questions
↳ Is zircon the same as cubic zirconia?
No. Zircon is a natural mineral. Cubic zirconia is a manufactured imitation of diamond.
↳ Why is tanzanite so rare?
It is found in only one small area of Tanzania, near Mount Kilimanjaro, which limits supply.