Iroishi Checker
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ReferenceREFERENCE
TanzaniteContribute a photo

Tanzanite

タンザナイト · たんざないと
NaturalPurpleBlue
Gemological dataPROPERTIES
Hardness6-7
Specific gravity3.35
Refractive index1.691-1.700
Crystal system斜方晶系
Color rangeCOLOR RANGE

Violet-blue, pure blue, and slightly purplish blue. Pure sapphire-blue stones (graded 'AAA' or 'AAAA' by the trade) command the highest prices; lighter or more violet stones are abundant.

UV responseFLUORESCENCE
Long-wave
365 nm
Inert
Short-wave
254 nm
Inert
Typical inclusionsINCLUSIONS
  • Generally clean — eye-clean stones are typical
  • nclusions when present
  • nclusions
  • nclusions (rare)
Optical characterOPTICAL TRAITS
  • Doubly refractive, biaxial positive
  • Strong trichroism: blue, violet, and burgundy red — diagnostic
What to look forID POINTS
  1. 01Strong three-color (blue / violet / burgundy) is the easiest field test — rotate through a dichroscope
  2. 02Soft material with distinct — chipped girdles or edges are common
  3. 03RI 1.691–1.700 distinguishes from sapphire (1.762–1.770) and iolite (1.522–1.578)
Stones it gets mistaken forSIMILAR STONES
Iolite
Iolite
アイオライト
Iolite has lower RI and shows trichroism of deep blue / pale yellow / nearly colorless — quite different from tanzanite's violet-burgundy axes.
Natural Blue Sapphire
Natural Blue Sapphire
ブルーサファイア（天然）
Sapphire is much harder (9 vs 6–7) and shows only two-color dichroism. RI is much higher.
Care & handlingCARE
  • Avoid ultrasonic and steam — thermal shock can cause
  • Avoid sharp impacts — distinct planes
  • Better suited to earrings, pendants, and occasional-wear rings than to daily wear
Market notesMARKET
PRICE RANGE

From $100/ct for small commercial material up to $1,500/ct for top color in larger sizes.

Note: Heat treatment is virtually universal and accepted; unheated stones are rare but command little premium. Color and saturation drive value far more than origin (which is fixed). Larger stones (>5 ct) with strong saturation rise non-linearly in price.

BackgroundBACKGROUND

Tanzanite is zoisite (Ca₂Al₃(SiO₄)₃(OH)) colored by trace vanadium. Nearly all rough is heat-treated at 380–500 °C to drive off the brownish component and bring out the saturated blue-violet color. Mohs 6–7 with distinct makes it more vulnerable to damage than its sapphire-like color suggests.

Origin & historyORIGIN & HISTORY

Origins

Found only at the Merelani Hills near Mount Kilimanjaro in Tanzania. The deposit is divided into four mining blocks and is expected to be depleted within 20–30 years, lending tanzanite a built-in scarcity narrative.

History

Discovered in 1967 by Maasai herder Ali Juuyawatu after a grass fire heated the surface deposits and revealed the saturated blue. Tiffany & Co. named the stone 'tanzanite' in 1968 and launched it as 'the most beautiful blue stone discovered in 2,000 years.' Added as a December birthstone in 2002.

Lore & symbolism

December birthstone (modern, alongside turquoise and blue zircon). Symbol of transformation and new beginnings. The 24th wedding anniversary stone.

OBSERVATION TOOLS · 3 ITEMS

Tools to confirm this stone

Tools that help confirm Tanzanite. Tap any item to jump to the matching section on the gem tools page.

References
最終確認日
2026年4月28日
参 考 文 献

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