Iroishi Checker
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ReferenceREFERENCE
Gray SpinelContribute a photo

Gray Spinel

グレースピネル · ぐれーすぴねる
NaturalBlack / Gray
Gemological dataPROPERTIES
Hardness8
Specific gravity3.58-3.63
Refractive index1.712-1.720
Crystal system等軸晶系（立方晶系）
Color rangeCOLOR RANGE

Pale silver-grey through medium steel-grey to deep platinum-grey and gunmetal-grey. The Mogok 'mauve-grey' historical material includes a faint warm brown undertone (hexcode #7A7570). Sri Lankan Ratnapura material is more uniformly cool grey (hexcode #6A7079). The 2007 Mahenge Tanzania premium grey material reaches a desirable 'platinum grey' or 'stormy silver' tone (hexcode #58606A).

UV responseFLUORESCENCE
Long-wave
365 nm
Generally inert (iron-chromophore material shows no Cr³⁺ )
Short-wave
254 nm
Generally inert
Typical inclusionsINCLUSIONS
  • egative crystals — diagnostic spinel signature at 10×
  • nclusion networks along healed fractures
  • nclusions of apatite, zircon, and rutile crystals
  • Iron-oxide stains along fracture surfaces in some Sri Lankan material
  • Synthetic Verneuil material: curved growth striae and round gas bubbles diagnostic
Optical characterOPTICAL TRAITS
  • Refractive index 1.712–1.736 — singly refractive isotropic cubic
  • Specific gravity 3.58–3.61
  • Mohs 8
  • No (isotropic cubic) — diagnostic against grey sapphire's distinct
  • Inert under both LW and SW UV — diagnostic against fluorescent grey moonstone
  • Sub-adamantine to vitreous lustre — produces excellent brilliance in well-cut stones
What to look forID POINTS
  1. 01Singly refractive (no under crossed polars) — diagnostic separator from grey sapphire (doubly refractive)
  2. 02egative crystals at 10× — diagnostic spinel signature
  3. 03Specific gravity 3.58–3.61 — separates from grey moonstone (2.55–2.58) and grey labradorite (2.69–2.72) decisively, and from grey sapphire (3.99–4.01)
  4. 04No — diagnostic against grey sapphire's distinct
  5. 05No adularescence or — diagnostic against grey moonstone and labradorite
  6. 06Mohs 8 — significantly harder than grey moonstone (Mohs 6) and grey labradorite (Mohs 6–6.5)
Stones it gets mistaken forSIMILAR STONES
Gray Sapphire
Gray Sapphire
グレーサファイア
egative crystals. Both species are popular engagement-ring central stones in the minimalist-jewelry trend; grey sapphire generally commands modestly higher prices than grey spinel at equivalent quality.
Gray Moonstone
Gray Moonstone
グレームーンストーン
Grey moonstone (orthoclase feldspar K(AlSi₃O₈), Mohs 6, SG 2.55–2.58, RI 1.518–1.526, doubly refractive biaxial negative, characteristic billowing adularescence 'moonstone sheen,' typically translucent to semi-transparent) versus grey spinel (Mohs 8, SG 3.58–3.61, RI 1.712–1.736, singly refractive isotropic cubic, no adularescence, transparent). The adularescence test is unambiguous: grey moonstone shows the characteristic billowing soft-glow sheen from internal albite-orthoclase lamellae while grey spinel shows transparent crystalline lustre without sheen. The specific-gravity difference (2.55–2.58 versus 3.58–3.61) and refractive-index difference (1.518–1.526 versus 1.712–1.736) are dramatic and diagnostic. The hardness difference (Mohs 6 versus 8) is decisive on scratch tests.
Labradorite
Labradorite
ラブラドライト
Labradorite (plagioclase feldspar Ca(Al₂Si₂O₈)·Na(AlSi₃O₈), Mohs 6–6.5, SG 2.69–2.72, RI 1.560–1.572, doubly refractive biaxial, characteristic spectral chiller' from internal albite-anorthite lamellae, typically translucent grey body) versus grey spinel (Mohs 8, SG 3.58–3.61, RI 1.712–1.736, singly refractive, no , transparent). The test (spectral colour flashes from internal lamellar diffraction) is diagnostic of labradorite; grey spinel shows no comparable optical effect. The specific-gravity difference (2.69–2.72 versus 3.58–3.61) and refractive-index difference (1.560–1.572 versus 1.712–1.736) are diagnostic.
Care & handlingCARE
  • Mohs 8 — excellent durability for daily wear including engagement-ring central stones
  • Ultrasonic cleaning generally safe for clean material
  • Steam cleaning acceptable
  • Storage in a soft pouch
Market notesMARKET
PRICE RANGE

Mahenge Tanzania premium 'platinum grey' material: $300–$3,000 per carat for fine clean 1–3 carat stones. Mogok Burmese 'mauve-grey' material: $200–$2,000 per carat. Sri Lankan Ratnapura material: $50–$500 per carat — the commercial bulk. Vietnamese Luc Yen material: $50–$400 per carat. Madagascar Ilakaka material: $30–$300 per carat. The 1–3 carat range is the sweet spot for engagement-ring central stones.

Note: Disclosure as 'natural spinel' is the trade standard; heat treatment is occasionally encountered (rarely effective for grey material) and must be disclosed under FTC Jewelry Guides §23.22 and CIBJO Blue Book. The minimalist-jewelry market drives most modern demand. Origin determination by GIA, AGL, Lotus Gemology, and SSEF distinguishes Mogok versus Mahenge versus Sri Lanka. The grey-spinel market is younger and smaller than the pink-spinel or grey-sapphire markets; pricing is correspondingly more accessible.

BackgroundBACKGROUND

Gray spinel is MgAl₂O₄ in the cubic isometric system, coloured by trace Fe²⁺ and Fe³⁺ substituting in the Mg²⁺ and Al³⁺ sites respectively, with possible trace Cr or V at much lower concentrations than in red/pink/purple/colour-change varieties. The iron-only or iron-dominant chromophore produces a characteristic 'steel grey' to 'platinum grey' colour without the warm pink or red component of Cr-bearing material. The Fe²⁺/Fe³⁺ ratio determines the tonal position: Fe²⁺-rich material trends toward bluer-grey (cool 'gunmetal' tones), Fe³⁺-rich material trends toward warmer brown-grey ('mauve grey' or 'mushroom grey' tones). The single refraction (isotropic cubic, RI 1.712–1.736, no , no ) is the diagnostic separator from grey sapphire (doubly refractive uniaxial negative with distinct grey-to-yellowish-grey ) and from grey moonstone (orthorhombic feldspar with characteristic adularescence/'moonstone sheen'). The Mohs 8 hardness and the high refractive index produce excellent brilliance and lustre in well-cut stones — the modern minimalist-jewelry market values these properties highly for engagement-ring central stones as an alternative to the more expensive grey sapphire or grey diamond.

Origin & historyORIGIN & HISTORY

Origins

Mogok Stone Tract in northern Myanmar (Mogok, Kyatpyin, Mansin) supplies the historic 'mauve-grey' premium reference. Sri Lankan Ratnapura district provides the bulk of commercial gray-spinel supply (the alluvial gem fields). Tanzania (Mahenge ward, Ulanga district — the 2007 Werner Spaltenstein discovery produced primarily pink but also steel-grey and platinum-grey material). Vietnam (Luc Yen, Yen Bai Province), Madagascar (Ilakaka), and the Pamir Mountains region (Tajikistan and Afghanistan) complete the source list. Mogok material trades at the premium tier; Sri Lankan material dominates the commercial market.

History

Gray spinel was largely an 'off-colour spinel' afterthought through most of the 20th-century gem trade — graded down from the red, pink, blue, and colour-change varieties as undesirable. The Sri Lankan Ratnapura alluvial mines supplied small volumes of grey material from at least the 18th century but the commercial market was always thin. The shift began with the 2007 Mahenge Tanzania discovery, which produced primarily neon-pink material but also supplied a cohort of fine steel-grey to platinum-grey stones that drew gemological attention. The decisive market repositioning occurred with the 2010–2015 minimalist-and-monochrome jewelry trend in Pinterest/Instagram engagement-ring culture — driven by independent designers (Anna Sheffield, Catbird, WWAKE in Brooklyn; Jennie Kwon in Los Angeles), the salt-and-pepper diamond engagement-ring trend, and broader 'anti-traditional' bridal preferences. Grey gem species (grey sapphire, grey moonstone, grey spinel, grey diamond) became premium engagement-ring central stones. Lotus Gemology and GIA began routinely issuing 'grey spinel' identification reports from c. 2012 onward; the term 'storm spinel' or 'stormy spinel' entered trade vocabulary in 2014–2016 designer marketing. The 2016 AGTA addition of spinel as August birthstone (alongside peridot and sardonyx) covered all colour varieties including grey.

Lore & symbolism

August birthstone since 2016 (AGTA addition). The grey colour carries modern minimalist-aesthetic associations rather than ancient traditional symbolism — 'restraint,' 'sophistication,' 'silver moonlight,' 'storm before clarity' in modern marketing. Modern metaphysical traditions (Melody 1995, Hall 2003) place grey stones on the throat chakra for communication and clarity. The Mogok 'Burmese mauve-grey' has accumulated a small premium-collector following.

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References
最終確認日
2026年4月28日
参 考 文 献

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