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Color Change Garnet
| Hardness | 7-7.5 |
| Specific gravity | 3.80-4.20 |
| Refractive index | 1.740-1.770 |
| Crystal system | 等軸晶系 |
Daylight: teal-blue, blue-green, gray-green. Incandescent: raspberry-red, purple-red, grape-purple. Vanadium and chromium are the color-change-active chromophores against a manganese-iron host.
- Pyrrhotite or other iron-sulfide crystals
- nclusions
- nclusions of zircon with tension halos
- nclusions are uncommon
- Singly refractive (cubic system) — no , no
- Refractive index 1.745–1.760 — at the high end of the pyrope-spessartine range
- Specific gravity 3.74–3.94 — increases with spessartine component
- Chelsea filter reaction reddish to pink — diagnostic of the vanadium-chromium activator combination
- 01Strong color change between D65 daylight and Illuminant A incandescent — the strongest natural color change in the garnet family
- 02Pink to red reaction under the Chelsea filter (vanadium-chromium signature)
- 03Singly refractive — separates from alexandrite (biaxial, strong ) and color-change sapphire (uniaxial, dichroic)
- 04Refractive index 1.75 separates from alexandrite (1.74–1.76 but with biaxial figure) and color-change sapphire (1.76–1.77)
- Mohs 7–7.5 — suitable for daily wear with normal care
- nclusions
- Stable to light and ordinary chemicals — the color change is permanent and is not affected by storage
About thirty thousand yen per carat for entry-grade Umba material up to several hundred thousand yen per carat for top Bekily stones above 2 ct with dramatic blue-to-raspberry shift.
Note: No treatments are recognized for color-change garnet; the stone is sold as-found and the dramatic color change is a natural property of the chemistry. Bekily material with a strong blue-green-to-raspberry shift carries a substantial premium over Umba green-to-brown stones. Sizes above 2 ct in fine color-change material are uncommon, and stones above 5 ct are major collector pieces.
Color-change garnet is a pyrope-spessartine solid-solution garnet — chemically intermediate between Mg₃Al₂(SiO₄)₃ and Mn₃Al₂(SiO₄)₃ — with trace vanadium and chromium producing a strong Usambara-effect color change between daylight (CIE D65, ~6500K) and incandescent illumination (Illuminant A, ~2856K). The variety was identified at Bekily in southern Madagascar in 1997 and described by Karl Schmetzer and others in Gems & Gemology in 1999. Earlier color-change pyrope-spessartine had been reported from Umba Valley (Tanzania) in the 1970s and from Tunduru in the 1990s, but the Bekily material produced the most dramatic shifts and became the type material for the variety. The cubic means there is no — the entire stone changes color at once, which gives the effect a uniform 'switch' character that alexandrite, with its strong , lacks.
Origins
Bekily in southern Madagascar is the type and benchmark locality, producing the most saturated and most dramatic color-change material. Umba Valley (Tanzania) was the historic source from the 1970s onward but the change is typically weaker — green to red-brown rather than blue-green to raspberry. Tunduru (Tanzania) and Sri Lanka produce smaller quantities. Norwegian and Kenyan localities have yielded sporadic material.
History
Color-change garnet was first recognized in the gem trade in the 1970s when Karl Schmetzer documented Umba Valley material that shifted from greenish to reddish-brown. The discovery of the Bekily deposit in 1997 transformed the category — the Madagascan stones showed an Usambara color change strong enough to rival fine alexandrite, and Gems & Gemology (Spring 1999, Schmetzer and Bernhardt) gave the variety its first thorough characterization. The trade has since adopted color-change garnet as a distinct commercial category, with prices for top Bekily material approaching the lower range of fine alexandrite.
Lore & symbolism
Garnets share the January birthstone designation (modern list, 1952). Color-change garnet is sometimes promoted in modern lapidary writing as the 'mood garnet' — a fanciful name not used by gemologists but common in retail descriptions of the Madagascan material.
Tools to confirm this stone
Tools that help confirm Color Change Garnet. Tap any item to jump to the matching section on the gem tools page.
- 最終確認日
- 2026年4月28日
- 参 考 文 献
- Gem Encyclopedia／ GIA (Gemological Institute of America)
- 宝石鑑別基準／ 中央宝石研究所 (CGL)
- Mineral & Gem Database／ Mindat.org / Gemdat.org
- 宝石学入門／ 全国宝石学協会
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