How Turquoise and Tanzanite differ in what they are, color, hardness and care.
| Turquoise | Tanzanite | |
|---|---|---|
| What it is | A soft, opaque blue to green gem colored by copper (blue) and iron or chromium (green). | The blue violet variety of the mineral zoisite, found only in Tanzania near Mount Kilimanjaro. It was discovered in 1967. |
| Birthstone for | December | December |
| Colors | Powdery blue to greenish robin's egg blue; Sky blue is often called "Persian blue" | Pale blue to intense ultramarine with violet undertones; Shows different colors from different angles |
| Mohs hardness | 5 to 6 | 6 to 7 |
| Toughness | Fair to good. | Fair to poor. It has cleavage and can break if struck. |
| Everyday wear | Delicate | Wear with care |
| Ultrasonic cleaner | Never | Never |
| Main sources | United States (now the largest supplier; Arizona leads), Iran (historic source of sky blue turquoise), Sinai Peninsula, Egypt (historic), Nevada, New Mexico, California and Colorado (US) | Tanzania only (a few square miles near Mount Kilimanjaro) |
| Common treatments | Some turquoise is treated to improve the surface; heat and solvents can damage treated surfaces. | Routinely heat treated to turn brownish crystals blue or violet; this is stable. |
Tanzanite is the harder of the two (6 to 7 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: Turquoise care and cleaning, AGS: Turquoise, GIA: Tanzanite care and cleaning, AGS: Tanzanite. Checked October 16, 2026.
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On the first of each month: that month's birthstone, what it means and how to care for it.
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