Tanzanite is one of the rarest gems on the planet, found in exactly one place: a narrow strip of land in the Merelani Hills of Tanzania, in the shadow of Mount Kilimanjaro. Discovered in 1967, it's the blue-violet variety of the mineral zoisite, and its color range — from deep indigo to soft periwinkle — shifts depending on the light. That's not a trick; tanzanite is trichroic, meaning it shows three distinct colors depending on the viewing angle. Pretty nerdy, but also pretty gorgeous.

Tiffany & Co. introduced tanzanite to the world in 1968, and in 2002 it became the first gem added to the official December birthstone list since 1912. It's a relative newcomer with serious staying power.