How Tanzanite and Zircon differ in what they are, color, hardness and care.
| Tanzanite | Zircon | |
|---|---|---|
| What it is | The blue violet variety of the mineral zoisite, found only in Tanzania near Mount Kilimanjaro. It was discovered in 1967. | A natural gem, not to be confused with man-made cubic zirconia. AGS calls it the oldest mineral on Earth: Australian zircons are about 4.4 billion years old. |
| Birthstone for | December | December |
| Colors | Pale blue to intense ultramarine with violet undertones; Shows different colors from different angles | Red; Orange; Yellow; Green; Blue (the December stone); Brown; Gold; Colorless |
| Mohs hardness | 6 to 7 | 6 to 7.5 |
| Toughness | Fair to poor. It has cleavage and can break if struck. | Fair to good, and can be brittle: facet edges can chip. |
| Everyday wear | Wear with care | Wear with care |
| Ultrasonic cleaner | Never | Not recommended |
| Main sources | Tanzania only (a few square miles near Mount Kilimanjaro) | Australia (about 37 percent of world supply), Thailand, Sri Lanka, Tanzania |
| Common treatments | Routinely heat treated to turn brownish crystals blue or violet; this is stable. | Commonly heat treated to make blue and colorless stones. |
Zircon is the harder of the two (6 to 7.5 on the Mohs scale). Both are December birthstones, so either makes a fitting gift. Choose by the color you love and how the piece will be worn; for a ring worn every day, the tougher stone will last better.
Sources: GIA: Tanzanite care and cleaning, AGS: Tanzanite, GIA: Zircon care and cleaning, AGS: Zircon. Checked October 16, 2026.
Birthstone of the month
On the first of each month: that month's birthstone, what it means and how to care for it.
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