Two gems are appropriate for December birthdays - Tanzanite and Zircon.
Discovered in the late 1960s in Tanzania, and found exclusively in this tiny area of the world, tanzanite exhibits a rich violet-blue color for which the gemstone is treasured; often it is heat-treated to achieve this color. Colors range from blue to purple, and tanzanites that are medium dark in tone, vivid in saturation, and slightly violet blue command premium prices. As tanzanite can be less expensive than sapphire, it often was purchased as an alternative. However, it has increased in popularity and now is valued more for its own beauty and brilliance than as a sapphire substitute.
Derived from the Arabic words zar and gun, meaning gold and color, zircon is found in a wide range of colors such as: blue, yellow, orange, brown, green, colorless, and red (the most prized color). For many years colorless zircon was used to imitate diamonds. Folk wisdom grants zircon the power to relieve pain, whet the appetite, protect travelers from disease and injury, to ensure a warm welcome, and to prevent nightmares guaranteeing a deep, tranquil sleep. Major sources of zircon are the Chanthaburi area of Thailand, the Palin area of Cambodia, and the southern part of Vietnam.
Source: American Gem Society