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UnderstandWhat it is, what people ask, how far this page goes
Natural inorganic gem materials · Mineral / gemstone variety · Natural identity; treatment status unknown
Cobalt Spinel
A blue to violet-blue variety of spinel coloured mainly by cobalt; the mineral species is still spinel. This page compares how the major standards and institutions name it, what must be disclosed when selling it, whether it can be worn every day, how it is treated and identified, and which source each conclusion comes from.
Price, rarity and origin are outside the scope of this wiki.
What this page can answer
This page covers
- How Cobalt Spinel forms and what gives its colourFormation setting, process and timescale; where its colour and optical effects come from, each finding graded and sourced
- How to identify Cobalt SpinelIdentification points from the research literature; how far lab testing can go and whether a synthetic exists
- Hardness, density and refractive index of Cobalt SpinelEach value with its source and check date
- Cobalt Spinel in English, Chinese and Japanese; national standard namesNames in four languages, the GB/T standard name and the suggested listing name; and: Which of GIA, FTC, CIBJO and Gem-A have a name for it on record, and do those agree?
- Listing and disclosing Cobalt SpinelThe listing name to use; what must be disclosed before sale
What we cannot conclude
- Whether one particular bead is natural, treated or synthetic — only a laboratory report can settle that.
- Geographic origin, unless an origin report accompanies the item.
- Price, rarity or investment value: this wiki covers naming and disclosure only.
Material research: formation, causes and history
What authoritative sources say about how this material forms, what causes its colour and optical effects, where its name comes from and how people have used it. Each statement carries an evidence grade and its sources; it describes the material in general, not any specific piece.
How it forms
Cobalt spinel is a blue to violetish blue variety of the mineral species spinel, its principal chromophore being cobalt (Co2+); it does not constitute a species in its own right. Spinel belongs to a family of metal oxides; its general formula is (A1−iBi)IV(AiB2−i)VIO4, where A denotes divalent cations (Mg2+, Fe2+, Zn2+, Mn2+, Co2+ or Ni2+ and so on) and B denotes trivalent cations (Al3+, Cr3+, V3+ or Fe3+ and so on); MgAl2O4 makes up most of gem-quality spinel. Co2+ in the lattice turns spinel blue, the colour being governed by transition-metal chromophores. In nature gem-quality spinel is mostly recovered from metamorphic rocks — marble, for example (such as the forsterite lenses of magnesian skarn in metamorphic sequences) — and from placers; cobalt-blue synthetic spinel can likewise be produced in the laboratory, by the Verneuil (flame-fusion) method.
Scope: Applies to explaining the identity, composition, colouration and occurrence of cobalt spinel as a blue variety of spinel, and notes that flame-fusion synthetic cobalt-blue spinel exists; not applicable to determining from the name whether a specific sample is natural or synthetic, or its locality or value.
Sources G&G Fall 2021 · G&G Fall 2022 · G&G Spring 2016
- Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions (Gems & Gemology, Fall 2021)
- Color Mechanism and Spectroscopic Thermal Variation of Pink Spinel Reportedly from Kuh-i-Lal, Tajikistan (Gems & Gemology, Fall 2022, Vol. 58, No. 3)
- Quench-Crackled Blue Synthetic Spinel (Gems & Gemology, Spring 2016)
Where it forms
Metamorphic setting: spinel occurs in metamorphic rocks such as marble, e.g. forsterite lenses of magnesian skarn in metamorphic series.
Sources G&G Fall 2021 · G&G Fall 2022 · G&G Spring 2016
- Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions (Gems & Gemology, Fall 2021)
- Color Mechanism and Spectroscopic Thermal Variation of Pink Spinel Reportedly from Kuh-i-Lal, Tajikistan (Gems & Gemology, Fall 2022, Vol. 58, No. 3)
- Quench-Crackled Blue Synthetic Spinel (Gems & Gemology, Spring 2016)
Placer (alluvial) setting: spinel also occurs in placer deposits.
Sources G&G Fall 2021 · G&G Fall 2022 · G&G Spring 2016
- Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions (Gems & Gemology, Fall 2021)
- Color Mechanism and Spectroscopic Thermal Variation of Pink Spinel Reportedly from Kuh-i-Lal, Tajikistan (Gems & Gemology, Fall 2022, Vol. 58, No. 3)
- Quench-Crackled Blue Synthetic Spinel (Gems & Gemology, Spring 2016)
How it forms, step by step
A metamorphic system containing Al, Mg and related components crystallizes spinel (MgAl2O4).
Transition-metal chromophores in the lattice (e.g. Co2+) give it a blue colour.
(Synthetic route) cobalt-blue synthetic spinel is grown from a melt by the Verneuil flame-fusion process.
Link to appearance
It appears as blue to violetish blue spinel, but colour and name cannot substitute for identification, which must distinguish natural from synthetic/treated material.
Sources G&G Fall 2021 · G&G Fall 2022
Timescale
The cited sources give no absolute age or growth duration for spinel.
Sources G&G Fall 2021 · G&G Fall 2022 · G&G Spring 2016
- Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions (Gems & Gemology, Fall 2021)
- Color Mechanism and Spectroscopic Thermal Variation of Pink Spinel Reportedly from Kuh-i-Lal, Tajikistan (Gems & Gemology, Fall 2022, Vol. 58, No. 3)
- Quench-Crackled Blue Synthetic Spinel (Gems & Gemology, Spring 2016)
Related base materials
- Spinel (MgAl2O4): Host mineral species; cobalt spinel is its blue variety coloured by Co2+
Supporting findings
Natural gem-quality spinel occurs largely in metamorphic rocks such as marble (e.g. forsterite lenses of magnesian skarn) and in placers.
Evidence grade AScope: Occurrence of spinel (including cobalt spinel); the specific origin requires separate determination.
Sources G&G Fall 2022 · G&G Fall 2021
Cobalt-blue synthetic spinel can be grown from a melt by the Verneuil (flame-fusion) process and must be distinguished from natural cobalt spinel in identification.
Evidence grade AScope: States that an artificial synthetic product exists; it does not conclude that any specific sample is synthetic.
Sources G&G Spring 2016
Recorded localities
Authoritative sources name a single or principal locality.
Africa
- TanzaniaListed as blue spinel source, not specifically cobalt-colored
Sources Gems & Gemology Spring 2015
Asia
- Luc Yen, Yen Bai, VietnamLeading source of vivid blue (cobalt-colored) spinel
Sources Gems & Gemology Spring 2015
- Sri LankaListed as blue spinel source, not specifically cobalt-colored
Sources Gems & Gemology Spring 2015
- MyanmarListed as blue spinel source, not specifically cobalt-colored
Sources Gems & Gemology Spring 2015
- PakistanListed as blue spinel source, not specifically cobalt-colored
Sources Gems & Gemology Spring 2015
These are localities recorded by authoritative sources, not an origin finding for any individual piece. The CIBJO Gemstone Book (2022, §4.2.3) says a place of origin names where a gem was mined or harvested, is a matter of opinion, does not imply a level of quality, and that cutting, processing or exporting centres must not be used to imply origin. See how far testing can go on this page, the origin determination guide and the overview of recorded localities.
Causes of colour and optical effects
Co2+-bearing spinel is commonly blue, its colour being determined by transition-metal chromophores (colour centres) in the lattice.
Evidence grade AScope: A colour-cause mechanism; distinguishing cobalt blue from other blue sources requires testing.
How it is identified
Appearance cannot confirm this material's identity or treatment state, and materials that look alike may differ in composition. Diagnostic measurable properties — such as spectral features and trace-element fingerprints (chemical fingerprints obtained with laboratory instruments such as LA-ICP-MS and EPMA) — must be determined by an accredited gemological laboratory; coatings and irradiation treatments must also be detected and disclosed at sale. This entry gives no self-test criteria: the material must be submitted for testing, and its identification cannot be inferred from appearance.
Evidence grade AScope: Conservative handling: no reliable synthetic/treatment comparator is available, so only the 'appearance cannot substitute for testing plus submit for testing' point is kept; testing must be performed by an accredited gemological laboratory.
Sources CIBJO Gemstone Book 2022 · G&G Spring 2019
Other research findings
Spinel belongs to a family of metal oxides whose general formula is (A1−iBi)IV(AiB2−i)VIO4 (here A denotes divalent cations — Mg2+, Fe2+, Zn2+, Mn2+, Co2+ or Ni2+ — and B for trivalent ones such as Al3+, Cr3+, V3+ or Fe3+). MgAl2O4 predominates in gem-quality spinel.
Evidence grade AScope: Composition of the spinel species; not a quantitative analysis of any sample.
Cobalt spinel is the blue to violetish blue variety of spinel whose main chromophore is cobalt (Co2+); it is not an independent mineral species.
Evidence grade BScope: An identity/variety-boundary judgement; it does not confirm any sample's cobalt content or chromophore attribution.
Limits of this research
- Research status: Formation, occurrence or other material-specific findings found in authoritative sources
- Cobalt spinel is a blue variety of spinel, not an independent mineral species; no specific sample is confirmed as natural or synthetic.
- Flame-fusion synthetic cobalt-blue spinel exists, and identification must distinguish natural from synthetic (e.g. PL Cr3+ shift; not expanded here).
- Not a judgement of origin, treatment, grade or value.
Methodology
- Origin determination and its limits
- Quality grading and value factors
- How gemmology became a technical discipline
Evidence grades
- A
- Standards bodies, government geological surveys, peer-reviewed research and museum records
- B
- Institutional educational material
- C
- Specialist databases or cautious readings
A statement is never graded above its strongest source.
This section is LumaLark's own factual restatement of public authoritative sources, credited item by item; it contains no verbatim excerpts, images or third-party logos.
DecideListing name, disclosure, care and treatments
- Suggested listing name
- Cobalt Spinel
IMA Mineral List 2026-07 “Spinel” · CIBJO Gemmological Laboratories Book 2024 §7.2.1.62 “Cobalt spinel”
Construction or treatment status
Natural identity; treatment status unknown
Related:Disclosure and cautions
This page cannot answer
Natural? · Origin · Price
A lab report settles these; this wiki covers naming and disclosure.
Related:What this page can answer
Answer at a glance
Cobalt Spinel's material identity has open questions that are not fully settled; this site lists it as "Cobalt Spinel" pending further verification.
Evidence
- CIBJO · 7.2.1.62
What this means for you
Before buying, check the recommended listing name "Cobalt Spinel" and any disclosed treatments on this page, and ask the seller for a grading report if in doubt.
Known uncertainty
- This entry's exact material identity is not fully settled.
- See “Disclosure and cautions” above
- Last reviewed
- 2026-09-26
Care and wear
No care facts are recorded for this entry itself. Its parent material has care records: see Spinel.
VerifyNames, standards, technical facts, clauses and sources
Names
Recommended listing nameThe suggested listing name for Cobalt Spinel is Cobalt Spinel. Institution usageCIBJO Gemmological Laboratories Book 2024 records the wording Cobalt Spinel; the FTC text on file has no wording for this name (checked), and GIA and Gem-A are unchecked; bodies without a recorded wording show the entry's own English name, which does not represent their position. Chinese standard nameThe Chinese standard naming counterpart is spinel (GB/T 16552—2017 Table A.1), and the name Cobalt Spinel itself is not listed in the original. Names in four languagesNames are given in Simplified Chinese, Traditional Chinese, English (Cobalt Spinel) and Japanese (pending verification); the wording of Japan's GSJ is not yet verified. Trade and mineralogical namesThe mineralogical name Cobalt spinel refers to the blue to violetish blue variety of spinel in which cobalt is the main colouring element.
- GSJ (Japan) formal name
- コバルト・スピネル（待核） (not yet checked for this body — the entry's own Japanese name is shown)
- GB/T naming counterpart (this name is not in the standard)
- 尖晶石 (GB/T 16552—2017 Table A.1)
- Mineralogical name
- Cobalt spinel: blue to violetish blue variety of spinel, cobalt as main chromophore
Four-language names
- 简体中文
- 钴尖晶石
- 繁體中文
- 鈷尖晶石
- English
- Cobalt Spinel
- 日本語
- コバルト・スピネル（待核）
See also: Misleading and prohibited trade names · Supplementary name index
Classification
- Origin
- Natural materials
- Material domain
- Natural inorganic gem materials
- Browsing family
- Oxide minerals
- Identity tier
- Mineral / gemstone variety
- Mineral chemical class
- Oxides / hydroxides
- Construction or treatment status
- Natural identity; treatment status unknown
What it is and how it's identified
Among the material facts for Cobalt Spinel, the composition (phase) is registered as spinel, from the CIBJO Gemmological Laboratories Book 2024; features such as chemical composition, fluorescence, UV-visible spectrum, infrared spectrum and magnification are given in the cited clauses for spinel (the whole mineral species), and are found in the material facts of the Spinel entry. Mohs hardness, density, refractive index and birefringence are taken from GB/T 16553—2017, whose cited clauses likewise cover spinel (the whole mineral species); these are class-level values, not measurements of Cobalt Spinel: Mohs hardness 8; density 3.57–3.7 g/cm³ (clause value 3.60, tolerance +0.10/−0.03, from which the limits are derived); refractive index 1.71–1.735 (clause value 1.718, tolerance +0.017/−0.008, from which the limits are derived), with further sub-grades in the clause and the overall value registered; and no birefringence. The body colour is blue to violetish blue, untreated; this site notes that the colour descriptions of azurite, iolite, benitoite and other entries in the CIBJO Gemmological Laboratories Book also mention blue or bluish colours.
Registered material facts
Each row carries its own source and check date and can be cited on its own; “—” means the cited source gives no value, not “none”.
Chemical composition, luminescence, UV-visible spectrum, infrared spectrum, magnification: these whole-class features are given in the cited clause for spinel (the whole mineral species), so they are not repeated on the Cobalt Spinel page; see the material facts on the Spinel entry.
Items below that name the class they cover give the cited clause’s value for that whole class, not a measurement of Cobalt Spinel (how to read class-level values).
Definition
Cobalt Spinel — composition (phase): spinel
CIBJO Gemmological Laboratories Book 2024
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Durability
Cobalt Spinel — Mohs hardness: 8
GB/T 16553—2017
Reference points on this site: Talc 1–3, Fluorite 4, Apatite 5–5.5, Orthoclase 6–6.5, Topaz 8, Diamond 10 (Source: GB/T 16553—2017); Gypsum 1.5–2, Calcite 3, Quartz 7 (Source: Handbook of Mineralogy); Corundum 9 (Source: GIA Gem Encyclopedia (care guide))
- Does this standard apply
- applies to this entry
- What this covers
- spinel (the whole mineral species)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.11 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Physical properties
Cobalt Spinel — density: 3.57–3.7 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- spinel (the whole mineral species)
- Qualification
The clause we cite gives 3.60, with a stated tolerance of +0.10 / -0.03. The range shown here is worked out from that.
- General note
- the clause has finer ranges
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.11 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Optical
Cobalt Spinel — refractive index: 1.71–1.735
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- spinel (the whole mineral species)
- Qualification
The clause we cite gives 1.718, with a stated tolerance of +0.017 / -0.008. The range shown here is worked out from that.
- General note
- the clause has finer ranges
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.11 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Cobalt Spinel — birefringence: none
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- spinel (the whole mineral species)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.11 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Cobalt Spinel — body colour: blue to violetish blue.
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- untreated
- Qualification
In chapter 7 of the CIBJO Gemmological Laboratories Book, the colour descriptions of Azurite, Iolite, Benitoite and other entries also name blue or a bluish colour.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
This material (RI / SG midpoints): 1.723 / 3.63; Closest values: 1Rhodochrosite 1.707 / 3.58, 2Alexandrite 1.749 / 3.73, 3Sinhalite 1.688 / 3.48, 4Pyrope 1.728 / 3.9, 5Vesuvianite / Idocrase 1.711 / 3.38
Show the full chart (330 registered materials)
Outside the full chart's range, drawn as triangles at the edge (RI / SG midpoints): Hematite 3.045/5.12, Synthetic Rutile 2.76/4.26, Rutile 2.753/4.23, Synthetic Moissanite 2.67/3.22
Testing and market
For untreated Cobalt Spinel, the basis for distinguishing it from other spinel varieties is that cobalt is the main chromophore. No synthetic Cobalt Spinel is available on the market.
How far testing can go
Cobalt Spinel — synthetic counterpart on the market: No synthetic counterpart of this material is commercially available
CIBJO Gemstone Book 2022
- Treatment state
- any treatment state
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Cobalt Spinel — criteria for distinction from other varieties: cobalt is the main chromophore.
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- untreated
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
Evidence and sources
Authority basis and clause sources
Sources
- CIBJO – The World Jewellery Confederation. Gemmological Laboratories Book (Blue Book), Gemmological Commission 2024-1.
- CIBJO – The World Jewellery Confederation. The Gemstone Book (Blue Book), 2022.
- SAMR / SAC (China). GB/T 16552—2017 Gems — Nomenclature.
- RRUFF Project, in partnership with the IMA – International Mineralogical Association. IMA Mineral List.
- eCFR (United States). 16 CFR Part 23 — Guides for the Jewelry, Precious Metals, and Pewter Industries.
Further reading
Related entries and topic cluster
Parent entry and related pages on this site. Rows marked “Planned” are suggested new content and have no link yet.
Related-entry tree for Spinel on this site: 3 entries listed by this site's parent-entry links; synthetic, treated and similar entries carry their recorded state after the name; this page (Cobalt Spinel) is marked.
- Spinel
Sub-entries (2)
- Cobalt Spinel
- Synthetic Spinel (Synthetic product)
This table scrolls sideways on narrow screens.
| Page | Content | Status |
|---|---|---|
| Browsing family | Oxide minerals | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Cobalt Spinel entry are maintained by the LumaLark wiki and matched one by one to the standard clauses or institutional sources they cite: every fact carries its source (with a clause or page locator) and a check date, so it can be traced back to the original. The entry exists so that buyers and sellers can check naming, disclosure and material facts item by item.