Tanzanite: The Vivid Violet-Blue of December's Birthstone
December is one of three months that gets multiple birthstones — tanzanite, turquoise, and zircon all share December — but tanzanite is the newest and most prized of the three. Discovered in Tanzania in 1967 and added to the modern birthstone list in 2002, tanzanite is found in only one place on earth: a 4-square-kilometer patch in the foothills of Mount Kilimanjaro. This guide covers what makes tanzanite unique, how to evaluate one, and why supply concerns are pushing prices higher every year.
In short: Tanzanite is December's rare blue-violet birthstone, found only in a 4-square-kilometer mining area in northern Tanzania. Its supply is geologically limited to roughly 20-30 more years, which is why prices have been rising 5-10% annually. Softer than sapphire (Mohs 6.5) but with dramatic colour change between blue, violet, and burgundy depending on viewing angle. A 1-carat AAA-grade tanzanite ring starts around $800-1,500.
What tanzanite is
Tanzanite is the blue-violet variety of the mineral zoisite (a calcium aluminum silicate). It scores 6.5 on the Mohs hardness scale — softer than sapphire or topaz, so it requires more careful wear. What sets tanzanite apart visually is pleochroism: the stone shows different colors when viewed from different angles. Most tanzanite displays blue, violet, and burgundy hues simultaneously, with the cut and orientation determining which dominates.
Why tanzanite is so rare
All tanzanite on earth comes from a single mining area in the Merelani Hills of northern Tanzania — roughly 4 square kilometers, no bigger than central Manhattan. Geological surveys estimate the deposit will be commercially depleted within 20 to 30 years at current extraction rates. That single-source rarity is what has driven tanzanite prices up steadily since the 1990s and is why fine specimens are increasingly considered collector items as well as jewelry stones.
Color grading for tanzanite
Tanzanite color is graded on saturation and hue. The most valuable stones display intense, vivid violet-blue (called "AAA" or "vivid" grade) with strong color visible without rotation. Lighter blue-purple shades ("A" or "AA" grade) cost less but lack the dramatic depth of top-tier tanzanite. Most tanzanite is heat-treated to enhance the blue tone — the process is industry-standard, stable, and disclosed on any reputable lab report. Untreated tanzanite exists but is rare and commands a premium.
