spinel
Enable an AI agent to identify spinel, assess its material condition and evidential certainty, and select justified examination, handling or processing actions.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to identify spinel, assess its material condition and evidential certainty, and select justified examination, handling or processing actions.
Spinel is the cubic oxide of end-member composition MgAl₂O₄ (space group Fd3m), type species of the AB₂O₄ spinel group, with Mg on tetrahedral sites and Al on octahedral sites in a cubic close-packed oxygen array; it is a high-temperature metamorphic and magmatic accessory, a historic gem species, and an industrial refractory and transparent ceramic.
It can be Select complementary optical, compositional and phase-identification examinations to resolve a spinel claim; Separate material identification from natural-origin, geographic-origin and treatment conclusions; Map fractures, inclusions and heterogeneous regions before selecting a sampling or cutting location; Assess whether cleaning, mounting or polishing is compatible with the observed condition and treatment evidence; Compare a spinel sample or batch with the optical, composition and defect requirements of a stated use; Refer ambiguous species boundaries, origin claims or treatment indications for specialist examination.
Distinguishing features
Combine composition with phase identification: the MgAl2O4 reference composition and cubic structure support spinel identification; a spinel-type diffraction pattern alone cannot establish the species. Reference: [Handbook of Mineralogy](https://www.handbookofmineralogy.org/pdfs/Spinel.pdf).
For transparent stones, test refractive behaviour rather than red colour: spinel is singly refractive, with a typical gem refractive index around 1.718; use corroborating evidence and record anomalous responses. Reference: [GIA Spinel](https://www.gia.edu/spinel?lang=en).
When refractive index or specific gravity differs from a typical spinel reference, investigate composition before rejecting identification: zinc substitution can shift both properties and cause confusion. Reference: [GIA Large Faceted Gahnospinel](https://www.gia.edu/gems-gemology/spring-2019-labnotes-large-faceted-gahnospinel).
Distinguish spinel material identity from natural origin: synthetic counterparts can share essentially the same chemical, physical and optical properties, so a basic identification result does not establish geological formation. Reference: [GIA Spinel](https://www.gia.edu/spinel?lang=en).
Examine different regions of a suspected assembled stone independently: identifying spinel in one component does not identify the whole object. Reference: [GIA Synthetic Sapphire and Synthetic Spinel Doublets](https://www.gia.edu/gems-gemology/winter-2016-labnotes-synthetic-sapphire-synthetic-spinel-doublets).
Scope
+ Identification of spinel against visually similar minerals, glass and other spinel-structure phases
+ Composition, substitutions and evidence supporting species assignment
+ Natural, synthetic or unresolved origin and treatment evidence
+ Individual crystals, rough and cut stones, grains, powders and consolidated magnesium aluminate material
+ Optical behaviour, internal defects and surface condition relevant to examination or use
+ Material-specific constraints on sampling, cleaning, cutting and processing
- The entire spinel supergroup or every compound with a spinel crystal structure
- Independent models of ruby, sapphire, garnet, glass and neighbouring mineral species
- Host-rock classification, deposit geology and mining operations
- Jewellery design, settings, ownership, pricing and transactions
- Complete ceramic manufacturing processes or finished optical and structural devices
Characteristics
- Material identity conclusion
- confirmed spinel | probable spinel | unresolved | excluded; evidence and confidence Prevents a colour, trade name or single measurement from becoming an unsupported identification.
- Major and minor element composition
- elemental atomic fractions or oxide mass %, with analytical method, location and uncertainty Tests magnesium-aluminium dominance and reveals substitutions or mixtures requiring a different assignment.
- Crystalline phase evidence
- linked diffraction or spectroscopic record, reference material and interpretation Connects an identity decision to evidence rather than treating the word spinel as proof.
- Physical form
- crystal | rough fragment | cut stone | grain | powder | consolidated body | component of assembly Determines which observations represent the material and which examination methods are feasible.
- Formation origin assessment
- natural | synthetic | unresolved; method or locality only when supported Separates mineral identification from claims about how or where the material formed.
- Treatment assessment
- detected | suspected | not detected by stated examination | untested; treatment type Avoids equating absence of detected evidence with proof that material is untreated.
- Refractive behaviour
- dimensionless refractive index, wavelength, temperature and observed polarisation response Supports discrimination from lookalikes while preserving measurement conditions and access limitations.
- Density or specific gravity
- kg/m³ for density or dimensionless specific gravity; method and uncertainty Provides corroborating identity evidence, with inclusions, porosity and mounting recorded as possible influences.
- Colour and spectral response
- colour under named illumination; absorption, transmission or emission versus wavelength in nm Records appearance and optical performance without inferring origin or colour-causing elements from hue alone.
- Internal and surface discontinuities
- mapped inclusions, fractures, chips, cavities, pores and suspected filled regions; dimensions in µm or mm Supports examination planning and assessment of whether proposed handling or processing could damage the material.
- Material extent and representativeness
- examined region or sample linked to parent stone, grain population or batch Prevents a result from one facet, grain or specimen being applied automatically to a composite or heterogeneous batch.
Also called
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.spinel
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 37 questions.
Spinel identity and naming boundary Establish what the spinel label denotes and whether the examined material supports that assignment.
Spinel can denote a particular material or a broader structural family; confusing these meanings creates incorrect catalogue identities.
Species and structure
Separate magnesium aluminate identity from membership in a structural family.
Composition and phase agreement
Record whether chemical and structural observations support the same identity, including unresolved disagreement.
- Does spinel here mean the MgAl2O4 species or only a spinel-structure phase? definition
- Which measured composition and phase-identification results support or contradict the assignment? measurement
- Could substitutions or additional phases require a neighbouring mineral or mixture model? boundary
Lookalike exclusion
Evaluate plausible alternatives for the observed stone or material.
Differential identification
Keep the competing identities and the observations that discriminate between them.
- Which alternatives remain plausible, such as corundum, garnet, glass or another spinel-group mineral? boundary
- What combination of refractive behaviour, density, spectra or composition separates those alternatives in this specimen? measurement
- Which next examination would resolve the remaining ambiguity with the least alteration? action
Composition and optical response Connect measured chemistry and optical behaviour without assuming that appearance uniquely determines composition.
Substitution and spatial variation affect identification and intended optical use.
Substitution and heterogeneity
Describe departures from the reference composition and variation within the examined material.
Chemical variation
Record measured Mg, Al and substituting elements with sampling locations and analytical limits.
- What major and minor elements were measured, and with what detection limits? measurement
- Do different zones or grains have compositions that undermine a single material assignment? boundary
Colour and transmission
Describe optical response under stated conditions and distinguish observations from causal interpretations.
Optical response evidence
Retain spectra and viewing conditions behind colour, transparency and fluorescence descriptions.
- What colour, transmission and fluorescence are observed under specified illumination and specimen thickness? measurement
- What evidence supports a proposed colour-causing element rather than a hue-based guess? provenance
- Does zoning or scattering prevent the examined region from representing the whole stone or body? boundary
Formation and treatment evidence Evaluate natural or manufactured formation separately from subsequent modification.
A valid spinel identification does not itself settle natural origin, geographic attribution or treatment history.
Natural or manufactured formation
Connect origin conclusions to diagnostic observations and traceable records.
Formation origin assessment
Record the basis and limits of natural or synthetic attribution, keeping geographic claims separate.
- Which inclusions, growth features, analytical results or production records support natural or synthetic formation? provenance
- Is a claimed locality supported independently of the conclusion that the material is natural? provenance
- What evidence is missing before origin can be assigned? boundary
Post-formation modification
Distinguish documented treatments from indications and untested possibilities.
Treatment evidence and detection limits
Record examination for heating or fracture filling without interpreting a negative examination as universal proof. Reference: [GIA Micro-Features of Spinel](https://www.gia.edu/gems-gemology/spring-2021-visual-guide-to-micro-features-of-spinel).
- What evidence indicates heating, fracture filling or another modification, and where is it located? measurement
- Which treatments could the examination detect, and which remain unresolved? boundary
- What proposed cleaning or processing action requires treatment uncertainty to be resolved first? action
Material form and integrity Describe how spinel occurs in the examined object and which discontinuities affect its condition.
A faceted crystal, a powder batch and a consolidated body require different interpretations of sampling, defects and bulk measurements.
Crystals, grains and assemblies
Establish whether observations concern one crystal, many grains or one part of a composite.
Extent of spinel material
Locate the identified spinel relative to host material, binders, other phases or joined components.
- Is the examined material a single crystal, grain population, consolidated body or component of an assembly? definition
- Which regions were actually identified as spinel, and which remain unexamined? measurement
- Does the whole object require a rock, composite or device model linked to this material? boundary
Fractures, inclusions and pores
Map internal features and damage relevant to stability and interpretation.
Integrity assessment
Distinguish observed inclusions, open fractures, chips and porosity from inferred consequences.
- Where are fractures, inclusions, chips or pores, and do they intersect exposed or proposed worked surfaces? measurement
- Which features are documented as pre-existing, newly formed or of unknown history? provenance
- Which features require changing a proposed sampling, cutting or mounting operation? action
Examination and use decisions Translate the spinel assessment into proportionate examinations and use-specific decisions.
Recognising spinel is insufficient to decide whether a particular specimen can be sampled, worked or accepted for an intended application.
Diagnostic access and sampling
Choose examinations that account for polish, mounting, opacity, grain size and acceptable alteration.
Next examination selection
Select a test for a stated unresolved claim and record its limitations for this physical form.
- How do mounting, surface finish, opacity or grain size restrict the proposed optical or analytical test? boundary
- Can a nondestructive examination resolve the claim, or is an explicitly authorised sample needed? action
- How will the tested facet, grain or subsample represent the material being assessed? measurement
Handling and application fit
Evaluate proposed actions against observed condition and explicit application requirements.
Condition-dependent action
Record an action decision with the material evidence and application limits that justify it.
- What optical, compositional or defect requirements must this spinel meet for its stated use? definition
- Do measured properties and examination coverage establish those requirements for this specimen or batch? measurement
- Given fractures, possible filling and physical form, may the proposed cleaning, polishing, cutting or thermal operation proceed? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Gem-quality magnesium spinel (transparent MgAl₂O₄)
- Rock-forming accessory spinel in metamorphic and magmatic rocks
- Ferroan spinel (pleonaste / ceylonite)
- Chromian red-to-pink gem spinel
- Cobalt-blue gem spinel
- Synthetic Verneuil (flame-fusion) and flux- or Czochralski-grown spinel
- Transparent polycrystalline MgAl₂O₄ ceramic
- Sintered or fused magnesia-spinel refractory grain and brick
- Which of these kinds and varieties hold for the sense of spinel this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q186890 - Item for the mineral species spinel (MgAl₂O₄), not the whole AB₂O₄ group.
- IMA-CNMNC - spinel (symbol Spl) - Grandfathered approved mineral name; Spl is the 2021 IMA symbol.
- Nickel-Strunz - 4.BB.05 - Oxide class; spinel group.
- Dana 8th - 7.2.1.1 - Multiple oxide, spinel subgroup, type species.
- CAS - 12068-51-8 - Magnesium aluminium oxide / magnesium aluminate, the chemical substance corresponding to MgAl₂O₄.
- EC (EINECS) - 235-098-1 - Same substance as CAS 12068-51-8.
- Which of these identifiers and schemes hold for the sense of spinel this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- IMA Commission on New Minerals, Nomenclature and Classification (CNMNC): approved mineral species name spinel and symbol Spl; Mg-dominant Al end-member only - chromite, magnetite, hercynite and gahnite are separate species.
- CIBJO Coloured Stone Commission, Coloured Stones Book: spinel is a gem species distinct from corundum; historic trade names such as balas ruby are not permitted as species names.
- ISO 10081-2 (ISO/TC 33, Refractories): classification of dense shaped basic refractory products, the class that includes magnesia-spinel bricks.
- ECHA / EU REACH: magnesium aluminium oxide (CAS 12068-51-8) is a registered chemical substance for manufacture and import.
- Which of these standards and regulation hold for the sense of spinel this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Faceted gemstones, including historic Crown Jewel stones long called rubies (e.g. the Black Prince's Ruby) that are red spinel from Badakhshan.
- Current gem production from Mogok (Myanmar), Mahenge (Tanzania), Lục Yên (Vietnam) and Sri Lanka, traded as red, pink, violet, blue and black spinel.
- Accessory mineral in marble, skarn, aluminous xenoliths, and as the aluminous phase in spinel-facies mantle peridotite (spinel lherzolite).
- Magnesia-spinel refractory brick and castable in steel-ladle linings and cement-kiln burning zones, chosen for thermal-shock resistance versus chrome-bearing magnesia brick.
- Hot-pressed or sintered polycrystalline MgAl₂O₄ as a transparent ceramic for armour windows and mid-IR optics.
- Flame-fusion synthetic spinel used as a cheap colourless or coloured gem simulant and as a technical single crystal.
- Which of these real-world use hold for the sense of spinel this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Mohs hardness - 8 - Mohs
- Specific gravity (end-member MgAl₂O₄) - 3.58-3.61 - g·cm⁻³
- Specific gravity (natural Fe- or Zn-bearing crystals) - 3.5-4.1 - g·cm⁻³
- Refractive index (isotropic n) - 1.712-1.736 - dimensionless
- Cubic cell edge a - 8.08-8.09 - Å
- Melting point (stoichiometric MgAl₂O₄) - 2105-2135 - °C
- Al₂O₃ in stoichiometric spinel - 71.7 - wt%
- Which of these typical measurements hold for the sense of spinel this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Trade and historic misidentification as ruby: red Cr-bearing spinel lacks dichroism and has lower RI and hardness than corundum, but can still be sold or catalogued as ruby.
- Synthetic Verneuil spinel (often non-stoichiometric, sometimes Co-doped) passed as natural spinel or as other gems; curved growth striae and gas bubbles are the usual giveaways.
- Octahedral parting and conchoidal fracture: hardness 8 does not prevent brittle chipping in jewellery or ballistic ceramics.
- In transparent spinel ceramic, residual porosity and grain-boundary scatter collapse visible/IR transmission and ballistic performance.
- In magnesia-spinel refractories, thermal-shock spalling and slag or clinker infiltration, plus hydration and crumbling of coexisting free MgO, are the usual lining failures.
- In-situ spinel formation in alumina-magnesia castables produces a volume expansion that can crack a lining if the recipe and firing schedule are wrong.
- Which of these failure modes and hazards hold for the sense of spinel this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Mineralogy restricts spinel to the Mg-dominant Al end-member; igneous and mantle petrology still say spinel for the whole group (as in spinel lherzolite, which is usually chromian spinel / chromite).
- European and Persian historic trade used balas ruby (from Balascia / Badakhshan, now Kuh-i-Lal, Tajikistan) for red spinel; that name is obsolete in modern gem nomenclature.
- Gem-origin labels (Burmese/Mogok, Mahenge, Vietnamese cobalt-blue, Ceylon) carry large price effects that chemical species does not.
- Ceylonite and pleonaste survive as locality or ferroan-variety names in older literature and in some European collections; they are not IMA species.
- In Japanese and European ceramics, spinel usually means manufactured MgAl₂O₄ refractory or transparent ceramic, not a gem crystal.
- Which of these regional variation hold for the sense of spinel this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Ruby / sapphire (corundum, Al₂O₃) - Corundum is uniaxial (anisotropic, dichroic), Mohs 9, RI about 1.76-1.77; spinel is isotropic (extinct in all positions in crossed polars), Mohs 8, RI about 1.72.
- Pyrope (and other red garnet) - Both are isotropic; pyrope typically has higher RI (near 1.74) and different absorption (iron-dominated) and inclusion suites; chemistry (Mg-Al oxide vs silicate) is decisive.
- Taaffeite / magnesiotaaffeite - Doubly refractive (uniaxial or biaxial) versus isotropic spinel; the usual bench test when a 'spinel' shows birefringence.
- Gahnite (ZnAl₂O₄) - Zn-dominant spinel-group species: distinctly higher SG (about 4.0-4.6) and typically green to blue-green; Zn versus Mg end-member by analysis.
- Hercynite (FeAl₂O₄) and chromite (FeCr₂O₄) - Separate IMA species on the spinel join; distinguished by Fe²⁺- or Cr-dominant chemistry, usually opaque, and (for chromite) ore-grade Cr content - not by crystal class.
- Magnetite (Fe₃O₄) - Inverse spinel, opaque and strongly ferrimagnetic; MgAl₂O₄ spinel is non-magnetic and typically transparent to translucent.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of spinel this model covers, and on what evidence? provenance
Sources
- Spinel (Gem Encyclopedia) - Gem species identity, typical RI/SG/hardness, colour causes (Cr, Co, Fe), localities, and the historic confusion with ruby.
- Handbook of Mineralogy: Spinel - Ideal formula MgAl₂O₄, cubic Fd3m cell, hardness, density, occurrence, and distinction from other spinel-group species.
- An Introduction to the Rock-Forming Minerals (spinel-group oxides) - Crystal chemistry of normal versus inverse spinels, solid solution toward hercynite, gahnite and chromite, and petrologic occurrence.
- IMA-CNMNC approved mineral symbols - Official IMA species name spinel and the symbol Spl.
What the second pass must settle
- Does vr.tr.spinel denote the mineral species, magnesium aluminate material including manufactured forms, or the broader structural family, and does an existing Vercy world model already own that concept?
- Which authoritative nomenclature criteria should govern substituted or nonstoichiometric material near the boundaries with neighbouring spinel-group species?
- Which validated combinations of observations distinguish natural, synthetic and heat-treated spinel across colours and manufacturing routes, and what are their detection limits?
- Should powders and consolidated magnesium aluminate ceramics remain material forms within this model or link to a separate registered ceramic model?
- Which application-specific acceptance criteria and handling limits can be supported for fractured, filled, porous or thermally processed spinel?