Color Change Spinel

Daylight (D65 fluorescent): blue, bluish-grey, greyish-violet, or pale violet — typical hexcode #4A5985 to #6B7AA8. Incandescent (2856K tungsten or candlelight): deeper violet, reddish-purple, or red-purple — typical hexcode #6E4A75 to #8B4A5C. The colour-change effect is generally weaker than alexandrite's dramatic green-to-red shift but distinctively visible to the trained eye.

• egative crystals — diagnostic spinel signature at 10×
• nclusion networks along healed fractures
• nclusions (Sri Lankan and Vietnamese material)
• Colour-zoning patches showing the variable Cr/V/Fe chromophore distribution

• Refractive index 1.712–1.736 — singly refractive isotropic cubic
• Specific gravity 3.58–3.63 — slightly broader range than red/pink/grey spinel due to compositional variation
• Mohs 8
• No pleochroism (isotropic cubic) — decisive diagnostic against alexandrite chrysoberyl which shows dramatic three-axis pleochroism
• Moderate-to-strong colour-change effect daylight-to-incandescent
• Weak-to-medium red LW-UV fluorescence in Cr³⁺-dominant material

1. 01No pleochroism — decisive single-test separator from alexandrite chrysoberyl (which shows dramatic green-purple-red three-axis pleochroism on the dichroscope)
2. 02Singly refractive (no doubling under crossed polars) — separator from doubly-refractive alexandrite and colour-change sapphire
3. 03egative crystals at 10× — diagnostic spinel signature
4. 04Specific gravity 3.58–3.63 — separates from alexandrite (3.70–3.75) and colour-change sapphire (3.99–4.01)
5. 05Refractive index 1.712–1.736 — separates from alexandrite (1.746–1.755), colour-change sapphire (1.762–1.770), and colour-change garnet (1.730–1.762 overlap requires combined testing)
6. 06Daylight-to-incandescent colour shift visible under standard D65 and 2856K illumination

Color-change spinel is MgAl₂O₄ in the cubic isometric system, coloured by mixed trace chromophores typically Cr³⁺ (Sri Lankan Embilipitya material — the classical 1985 Schmetzer/Henn finding) or alternatively V³⁺ (rare V-dominant variety from Tajikistan) producing the alexandrite-like daylight-to-incandescent colour shift. The colour-change effect is driven by the same mechanism as alexandrite: the chromophore produces strong transmission in both the blue-green and the red regions of the visible spectrum with a relative absorption minimum in the yellow-orange — under blue-rich daylight illumination the blue-green transmission dominates and the stone appears blue/green/grey; under red-rich incandescent illumination the red transmission dominates and the stone appears purple/red. The single refraction (isotropic cubic, RI 1.712–1.736, no birefringence, no pleochroism) is decisively diagnostic against alexandrite (chrysoberyl, doubly refractive biaxial positive with dramatic three-axis pleochroism showing green-purple-red distinct directional colours). The Mohs 8 hardness and high refractive index produce excellent brilliance. The 1985 Karl Schmetzer / Henn paper at the German Diamond and Stone Examination Foundation (DSEF) Idar-Oberstein established the species as a distinct gemological variety; subsequent material from Kuh-i-Lal Tajikistan (V-dominant variant) and Vietnamese Luc Yen has extended the known compositional range.

Tools to confirm this stone

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

• 10倍ルーペDETAILS →

  内包物・カット痕・色ムラを観察する基本道具

• 強力ペンライトDETAILS →

  白色光と白熱光で色変化（カラーチェンジ）を観察

• 分光器DETAILS →

  クロム・鉄・コバルト由来の吸収線パターンで因元素を特定

• 屈折計DETAILS →

  屈折率（1.712–1.736）で鉱物種を絞り込み