opal
Enable an agent to recognise opal, assess its material and gemological state, and select suitable identification, handling, and use 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.
recalled by Codex without web access - no source was read
Researched by: Codex
Purpose and description
Enable an agent to recognise opal, assess its material and gemological state, and select suitable identification, handling, and use actions.
Opal is a naturally occurring hydrated silica mineraloid, conventionally written SiO₂·nH₂O, whose silica structure ranges from amorphous to poorly crystalline and which may exhibit play-of-colour.
It can be Select identification observations or laboratory tests that resolve specific uncertainties.; Classify optical behaviour while preserving lighting and viewing conditions.; Assess whether cleaning, wetting, drying, heating, or storage changes are appropriate for the specimen.; Evaluate suitability for cutting, polishing, mounting, or specimen preservation.; Record origin and treatment disclosures with supporting evidence.; Monitor cracking, colour, transparency, and mass for changes over time..
Distinguishing features
Establish hydrated silica identity and structural evidence rather than identifying opal solely from colour or trade name.
Distinguish play-of-colour from body colour, surface iridescence, and isolated reflections; absence of play-of-colour does not by itself exclude opal.
Assess natural versus synthetic origin separately from whether the material is opal; distinguish both from imitations.
Inspect interfaces to distinguish a single opal piece, opal attached to host rock, and an assembled doublet or triplet.
Test or document water uptake separately from appearance; hydrophane behaviour must not be assumed for every specimen.
Scope
+ Hydrated silica composition, water content, impurities, and structural classification
+ Natural or synthetic origin and evidence supporting identification
+ Play-of-colour, body colour, transparency, and optical uniformity
+ Porosity, water uptake, cracking, and changes under environmental exposure
+ Treatments, matrix relationships, and suitability for specimen or gem use
- Quartz, chalcedony, glass, and other materials mistaken for opal
- Complete geological deposits and mining operations
- Jewellery settings and finished jewellery products
- Backing materials, adhesives, and protective caps in assembled stones
- Commercial valuation, ownership, and trading transactions
Characteristics
- Material identity
- opal confirmed | opal suspected | imitation | unresolved Controls whether this model applies and how confidently subsequent actions can proceed.
- Origin
- natural | synthetic | unresolved Supports accurate identification and disclosure without conflating synthetic opal with imitation.
- Water content
- mass %, with analytical method and specimen conditioning Characterises the material while distinguishing measurements made under different conditions.
- Structural classification
- reported analytical class, method, confidence, or unclassified Separates measured internal structure from appearance-based variety names.
- Play-of-colour
- present | absent | uncertain; colours, pattern, viewing angles, and illumination Records a defining optical distinction among opal varieties.
- Body appearance
- body colour, tone, and transparency under stated observation conditions Prevents body colour from being confused with play-of-colour or treatment effects.
- Water uptake
- mass change %, exposure duration, liquid, temperature, and recovery conditions Supports assessment of hydrophane behaviour and exposure sensitivity when testing is appropriate.
- Physical condition
- intact | cracked | crazed | chipped | altered; location and extent Determines handling needs and whether processing may worsen damage.
- Treatment status
- untreated supported | treatment detected | treatment reported | unknown; treatment type Affects interpretation of appearance, stability, care, and disclosure.
- Material associations
- host rock, matrix, backing, cap, adhesive, or none observed Locates the opal boundary and identifies components requiring separate assessment.
Also called
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.opal
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 19 findings · 29 questions.
Opal identity Establish whether the material is opal and define the physical extent of that identification.
Appearance alone cannot resolve opal identity, origin, or composite construction.
Silica and water
Connect material identification to composition and structural evidence.
Identity evidence
Record evidence supporting hydrated silica identification and any unresolved alternative.
- What observations or analyses support identifying this material as opal rather than glass, quartz, or another silica material? definition
- What composition, water-content, or structural measurements exist, and how were they obtained? measurement
Specimen boundaries
Separate opal from associated geological and manufactured components.
Opal-bearing components
Locate opal within a specimen, matrix, or assembled stone.
- Is the examined object entirely opal, opal within or attached to host rock, or an assembled stone? boundary
- Which visible or tested interfaces separate opal from matrix, backing, adhesive, or a cap? measurement
Optical expression Describe opal appearance through reproducible observations.
Opal variety and practical gem use depend on optical behaviour that changes with observation conditions.
Play-of-colour
Characterise the presence and distribution of changing spectral colours.
Directional colour observation
Document colour changes with illumination and orientation without assuming their cause from a single image.
- Is play-of-colour visible, and under which illumination and viewing angles? measurement
- How were play-of-colour, surface reflections, and other iridescent effects distinguished? boundary
Body appearance
Separate underlying colour and transparency from directional optical effects.
Appearance classification
Record descriptive appearance and the criteria behind any variety or trade name.
- What body colour, tone, and transparency are observed under stated lighting and background conditions? measurement
- Which criteria support labels such as precious, common, fire, or black opal, and can more than one label apply? definition
Water and integrity Assess water interaction, environmental response, and physical damage.
A specimen's exposure response and existing damage determine which handling actions are suitable.
Water response
Distinguish documented hydrophane behaviour from untested assumptions.
Uptake and recovery
Record known water uptake and associated appearance changes, including reversibility.
- What evidence establishes whether this specimen exhibits hydrophane behaviour? measurement
- Would a wetting test risk alteration, and what existing evidence or less intrusive observation could answer the question? action
Damage and change
Track cracks and other alterations against exposure history.
Integrity baseline
Establish specimen-specific condition and distinguish observed change from proposed causes.
- Where are cracks, crazing, chips, or altered areas, and what observations establish their extent? measurement
- What changes followed documented temperature, humidity, liquid, or storage exposures, and which causal explanations remain uncertain? provenance
Origin and enhancement Evaluate natural or synthetic origin, geographic claims, and treatment history.
These claims affect recognition, care, and disclosure but require distinct supporting evidence.
Formation and source
Distinguish origin determinations from locality assertions.
Origin claims
Attach confidence and evidence to natural, synthetic, and geographic origin claims.
- What evidence supports natural or synthetic origin, and which identification limitations remain? provenance
- Is a claimed locality supported by collection records, laboratory evidence, a supplier statement, or no traceable evidence? provenance
Treatment evidence
Record interventions that may affect appearance or material behaviour.
Enhancement status
Distinguish detected or reported treatments from unknown treatment status.
- Is there evidence of dyeing, impregnation, smoke or sugar treatment, coating, or another intervention? measurement
- What treatment records or test limitations affect whether the specimen can be described as untreated? provenance
Handling and working Translate identification and condition into specimen-specific care and processing decisions.
Useful opal assessment must connect material evidence to actions an agent can recommend or defer.
Care decisions
Choose cleaning and storage practices from documented specimen behaviour.
Exposure suitability
Assess proposed care actions against water response, treatments, and construction.
- Which cleaning liquids, cleaning methods, and storage conditions are supported for this specimen's condition and treatment status? action
- Which uncertainties about water uptake, coatings, or bonded components require specialist assessment before care proceeds? action
Lapidary suitability
Assess opal-specific constraints on cutting, polishing, and mounting.
Working plan
Connect colour orientation, opal thickness, matrix, and fractures to a proposed working action.
- How do colour orientation, opal-bearing thickness, matrix boundaries, and fractures constrain cutting or polishing? action
- What controls are required for generated dust and process heat, considering the identified opal, host rock, and treatment materials? 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.
Check these first
Recalled without web access and unsourced; every item is a lead to verify.
- This describes the geological and gemological material; the listed varieties overlap rather than forming mutually exclusive classes.
- Property ranges are approximate recall values; porosity, water content, inclusions and host rock can affect measurements.
- Verify current CIBJO wording and specimen-specific treatment, origin and structural classification before formal publication.
- Which of these check these first hold for the sense of opal this model covers, and on what evidence? provenance
Kinds and varieties
Recalled without web access and unsourced; every item is a lead to verify.
- Precious opal: exhibits play-of-colour
- Common opal: lacks play-of-colour
- Fire opal: yellow, orange or red body colour, with or without play-of-colour
- Black opal: dark body tone
- Boulder opal: opal retained with its natural host rock
- Hydrophane opal: porous opal that absorbs water, potentially changing transparency and appearance
- Which of these kinds and varieties hold for the sense of opal this model covers, and on what evidence? provenance
Identifiers and schemes
Recalled without web access and unsourced; every item is a lead to verify.
- Chemical formula - SiO₂·nH₂O - Conventional compositional notation; water content varies, so this is not a fixed molecular formula.
- Which of these identifiers and schemes hold for the sense of opal this model covers, and on what evidence? provenance
Standards and regulation
Recalled without web access and unsourced; every item is a lead to verify.
- CIBJO, the World Jewellery Confederation, publishes the Gemstone Book covering gemstone nomenclature and disclosure, relevant to natural, synthetic, treated and assembled opal.
- Which of these standards and regulation hold for the sense of opal this model covers, and on what evidence? provenance
Real-world use
Recalled without web access and unsourced; every item is a lead to verify.
- Gemstones in jewellery, commonly cut as cabochons
- Decorative carvings and ornamental objects
- Mineralogical collections and geological research
- Research into structural colour and naturally occurring photonic structures
- Which of these real-world use hold for the sense of opal this model covers, and on what evidence? provenance
Typical measurements
Recalled without web access and unsourced; every item is a lead to verify.
- Mohs hardness - 5.5-6.5 - Mohs scale
- Refractive index - Approximately 1.37-1.47 - dimensionless
- Density - Approximately 1.98-2.25 - g/cm³
- Which of these typical measurements hold for the sense of opal this model covers, and on what evidence? provenance
Failure modes and hazards
Recalled without web access and unsourced; every item is a lead to verify.
- Some opals develop crazing, a network of cracks associated with water loss or environmental changes.
- Brittleness makes opal vulnerable to impact damage, chipping and fracture.
- Moderate hardness permits scratching and abrasion during wear.
- Porous hydrophane material can absorb liquids, causing changes in appearance or staining.
- Cutting and grinding generate dust requiring control; host rock may contain crystalline silica.
- Which of these failure modes and hazards hold for the sense of opal this model covers, and on what evidence? provenance
Regional variation
Recalled without web access and unsourced; every item is a lead to verify.
- Australian deposits include commercially important black, white and boulder opal.
- Ethiopian deposits include commercially important hydrophane opal, although origin alone does not establish absorption behaviour.
- Mexico is particularly associated with fire opal.
- Which of these regional variation hold for the sense of opal this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Recalled without web access and unsourced; every item is a lead to verify.
- Quartz - Quartz has a well-defined crystalline SiO₂ structure; opal is hydrated silica with amorphous or poorly crystalline structure.
- Chalcedony - Chalcedony is microcrystalline silica dominated by quartz-related structures rather than opal's hydrated, disordered silica structure.
- Synthetic opal - Synthetic opal is manufactured rather than geologically formed; distinguishing specimens may require microscopic and laboratory examination.
- Opal doublet or triplet - These are assembled products combining an opal layer with backing and, for triplets, a transparent cap.
- Opalite glass - Opalite glass is manufactured glass marketed for its opalescent appearance, rather than natural opal.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of opal this model covers, and on what evidence? provenance
What the second pass must settle
- Which authoritative terminology and analytical criteria should govern opal structural classes and overlapping gemological variety names?
- Which identification methods reliably distinguish natural opal, synthetic opal, imitations, and treatments across the varieties covered?
- What specimen-specific evidence can support environmental care limits and predictions of cracking or irreversible appearance change?
- Which CAS, EC, or other substance identifiers apply to particular opal materials, and when would using a generic silica identifier misrepresent them?
- Which occupational exposure requirements apply when working opal with different host rocks, impurities, and treatments?