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Natural inorganic gem materials · Mineral / gemstone variety · Natural identity; treatment status unknown

Boulder Opal

A variety in which a thin layer of natural Opal is attached to an ironstone or sandstone host rock; it is not a composite stone, but whether the host rock is genuine must be tested. 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.

Edited by RalphReviewed by JuneLast updated 2026-10-12Who maintains this page

Care and wear

What this page can answer

This page covers

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

Boulder opal is an opal variety in which a thin layer of natural opal lies on a host rock such as ironstone or sandstone, pieces of that host (the matrix) being incorporated into the cut gem. Formation is natural: water carrying silica leaves silica within cracks and among the beds of ancient sedimentary rock such as sandstone, producing a thin opal seam that sits alongside the host rock. Opal is separated by geological setting into 'sedimentary-type' (the numerous Australian occurrences of the Great Artesian Basin among them) and 'volcanic-type'. Because boulder opal carries matrix, its finished gems always contain matrix; the host rock coexists with the opal in nature rather than being a layer bonded on artificially.

Scope: Applies to natural boulder/matrix opal containing host rock; does not apply to solid opal without host rock, and is not equivalent to black opal or to man-made assembled stones such as doublets.

Sources GIA Opal Description · G&G Winter 2023 · G&G Spring 2018 +1

Where it forms

Cracks and interlayer spaces of ancient sedimentary rock (such as sandstone or ironstone host rock); Queensland’s boulder opal belt in Australia

Sources GIA Opal Description · G&G Winter 2023

How it forms, step by step

  1. Silica-bearing water penetrates sedimentary rock such as sandstone and deposits silica in cracks and between layers.

    Sources GIA Opal Description

  2. A thin opal seam forms and naturally coexists and consolidates with the host rock (matrix).

    Sources GIA Opal Description

  3. During cutting, the host-rock matrix is incorporated into the gem, producing matrix-bearing boulder opal.

    Sources GIA Opal Description

Link to appearance

Boulder opal’s play-of-color comes from diffraction by ordered silica spheres within the thin opal seam; the host-rock matrix both provides contrast and becomes part of the finished gem, defining its appearance.

Sources GIA Opal Description

Timescale

The cited sources give no absolute timescale for boulder opal formation.

Sources G&G Winter 2023

Supporting findings

Boulder opal takes the form of a narrow opal seam resting on a host rock, sandstone for example; it develops when water carrying silica leaves silica behind within cracks and among the beds of sedimentary rock.

Evidence grade A

Scope: Describes sedimentary-pathway formation using sandstone as the example; ironstone-host detail is not expanded.

Sources GIA Opal Description

Geologists separate opal by its geological setting into a 'sedimentary-type'—the numerous Australian occurrences within the Great Artesian Basin belong here—and a 'volcanic-type'. Boulder opal belongs to the sedimentary host-rock setting.

Evidence grade A

Scope: A classification framework; assigning a specific deposit requires case-by-case verification.

Sources G&G Winter 2023

Recorded localities

Authoritative sources name a single or principal locality.

Locality sketch mapLand outlines only; the map does not depict any national or regional boundary. Dots mark approximate positions. Base map: Natural Earth (public domain).

Oceania

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

Boulder opal shows play-of-color by the same route as precious opal: monodisperse, regularly packed nanoscale silica spheres form a three-dimensional diffraction grating, white light is diffracted into spectral hues that shift with viewing angle, and sphere diameter determines which colour appears—larger spheres tending red, smaller ones green.

Evidence grade A

Scope: The mechanism applies to the play-of-color shown by boulder opal and explains the optical origin only; it does not establish locality, natural origin, or treatment of any particular stone.

Sources G&G Fall 2013 · G&G Summer 2025

The play-of-color comes from the sphere grating inside the opal layer, not from the host rock or matrix: boulder opal is a thin opal seam resting on host rock (often ironstone or sandstone), and the darker surround serves only as a backdrop that sets off the flashes rather than generating diffracted colour itself.

Evidence grade A

Scope: The statement locates the optical origin of the flashes in the opal layer rather than the surrounding rock; it does not address the precise lithology of the host or establish locality, natural origin, or treatment.

Sources GIA Opal Description

How it is identified

Boulder opal is a thin layer of opal on a host rock, and by sight it can be hard to tell from put-together or imitation material. Deciding whether a specimen is natural, laboratory-made or composite/imitation calls for laboratory measurement of its gemological properties and composition rather than appearance alone. The conclusion should be issued by a qualified gem laboratory.

Evidence grade A

Scope: Applies where natural, synthetic and imitation opal must be distinguished; no self-administered criteria are given.

Sources G&G Fall 1987 · CIBJO Gemstone Book 2022

Other research findings

Boulder opal is natural opal that ranges from translucent to opaque and shows play-of-color over a pale-to-dark background; pieces of the enclosing rock—termed matrix—end up incorporated in the cut gem.

Evidence grade A

Scope: A GIA varietal description; it includes the key feature that matrix is incorporated into the finished gem.

Sources GIA Opal Description

Australian boulder opal production is quite low; material from Queensland’s boulder opal belt can be cut to include matrix together with rhyolite rock.

Evidence grade B

Scope: Market and cutting statements from a trade interview, not systematic production statistics.

Sources G&G Spring 2018

Boulder opal’s matrix coexists naturally with the opal; it is not a composite layer assembled by bonding or other artificial methods, and so it should be distinguished from artificial composites such as doublets.

Evidence grade A

Scope: A distinction by contraposition grounded in the definition of composite stones as artificially assembled; it does not cover doublet construction.

Sources CIBJO Coral Information Sheet · GIA Opal Description

Limits of this research

  • Research status: Formation, occurrence or other material-specific findings found in authoritative sources
  • The cited sources give no absolute timescale for boulder opal formation and do not systematically cover localities outside Queensland.
  • The name ‘boulder opal’ can be confused with ‘black opal’ and ‘doublet’; this entry defines it from the cited sources as a natural matrix-bearing variety only.

Methodology

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
Boulder Opal (natural host rock retained)

IMA Mineral List 2026-07 “Opal” · CIBJO Gemmological Laboratories Book 2024 §7.2.1.32 “Boulder opal”

Construction or treatment status

Natural identity; treatment status unknown

Treatments recorded for this material: Filled / Fracture-filled, Dyed (via parent material), Coated (via parent material)

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

Not an assembled stone; polymer filling of the voids must be disclosed and the authenticity of the host rock must be verified by testing.

Evidence

  • CIBJO · 7.2.1.32

What this means for you

Before buying, check the recommended listing name "Boulder Opal (natural host rock retained)" and any disclosed treatments on this page, and ask the seller for a grading report if in doubt.

Known uncertainty

Last reviewed
2026-09-01

Care and wear

Normal care for every gemstone (CIBJO Gemstone Book §6.1), in brief:

  • Handle it gently.
  • Store pieces apart when not worn, so they cannot scratch each other.
  • Clean with warm soapy water and a soft brush.
  • Use ultrasonic cleaners only with caution.

The §6.1 wording and the full list of §6.2 special-care letters cited on this page are on the general gem care page.

The item-by-item care advice that the GIA Care and Cleaning Guide gives for the whole class, and so for Boulder Opal, is set out in full under care on the Opal entry.

Care

Boulder Opal — care (chemicals): Treatments with dye, oil, resin, wax or plastic are not permanent; keep it away from all solvents (including dish-washing liquids), chemicals and heat.

CIBJO Gemstone Book 2022

CIBJO Gemstone Book §6.2:special-care code k

Treatment state
treated
Only after these treatments
filling
Source & check 2026-09-25
Source
Fact checked on
2026-09-25

Boulder Opal — care (special care): unhardened colourless substances in voids: special care (SC); avoid heat and ultrasonic cleaning, and do not repolish.

AGTA Gemstone Information Manual, 17th ed.

Treatment state
treated
Only after these treatments
fissure filling with oil, fissure filling with resin
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.

Common care questions and matching entries

ChemicalsFor the care of Boulder Opal, the chemicals point is registered from the CIBJO Gemstone Book (2022): for treated Boulder Opal, in the case of filling only, treatments with dye, oil, resin, wax or plastic are not permanent, so it must be kept away from all solvents (including detergent), chemicals and heat. Special careThe special care point is registered from the American Gem Trade Association (AGTA) Gemstone Information Manual, 17th edition: for treated Boulder Opal, in the case of oiled fissures and resin-filled fissures only, if colourless unhardened substances have entered the voids it is classed as special care (marked SC), and it must be kept away from heat and ultrasonic cleaners and should not be repolished. CleaningThe Gemological Institute of America (GIA) care and cleaning guide is given for the whole class, and its point-by-point advice is listed in the care section of the Opal entry.

This table scrolls sideways on narrow screens.

QuestionMatching entries
Contact with acids, alkalis and household chemicalsTreatments with dye, oil, resin, wax or plastic are not permanent; keep it away from all solvents (including dish-washing liquids), chemicals and heat

Care entries by treatment state

The same entries grouped by the treatment state each applies to; each links to its full wording and source. Letters are CIBJO special-care codes, explained on the gemstone care page.

treated (Only after these treatments: filling)

treated (Only after these treatments: fissure filling with oil, fissure filling with resin)

Treatments and identification leads

One row per treatment, with three standards side by side: how often it occurs and how stable it is (CIBJO), its category in GB/T 16552—2017 Table B.1 (this site's paraphrase) and how the JJA/AGL 2025 table lists it. Each CIBJO value links to its entry under “Testing and market”, where the wording and source are given in full.

This table scrolls sideways on narrow screens.

TreatmentMarket frequency (CIBJO)Stability (CIBJO)GB/T 16552 categoryJJA/AGL listingIdentification leads
Filling——Graded — see §5.4.1, Table 1——
Dyeing——Treatment——
Coating——Treatment——
filling of the host rock———filling of the host rock—

“—” means the cited source gives no value for that item, not “none”. Source: GB/T 16552—2017 Table B.1 (row for Opal); JJA/AGL 2025

Whether a treatment has to show in the name differs between the two rule sets (this site’s paraphrase):

  • GB/T 16552—2017: a method classed as treatment has to be stated in the name itself — the method put before the name, or added in brackets after it; a method classed as optimization does not need to appear in the name, though one marked “Optimization (annotation required)” still has to be noted in the quality documents. Source: §5.4.2.1 a), b); §5.4.2.2 a)
  • CIBJO Gemstone Book 2022: no longer splits treatments into ones that need specific disclosure and ones that need only general disclosure: every treatment is to be disclosed, and the seller tells the buyer which treatment was used and what special care it calls for. Source: §4.2.5 Note 2, §4.2.5.1, pp.14–15

What this table covers

What this page can give

  • Registered treatments, their stability and how often they occur (see the table above)
  • Identification leads for each treatment, for use when sending a stone for testing

VerifyNames, standards, technical facts, clauses and sources

Names

Standard and listing namesThe suggested listing name for Boulder Opal is "Boulder Opal (natural host rock retained)". The national-standard naming counterpart is opal (GB/T 16552—2017 Table A.2); the text does not list the name Boulder Opal. Names in four languagesThe names cover Simplified Chinese, Traditional Chinese, English (Boulder Opal) and Japanese; the Japanese name is the entry's own, and the GSJ (Japan) wording for it has not yet been checked. Trade and mineralogical namesThe mineralogical name is described as a thin layer of natural opal on an ironstone or sandstone host rock. The Australian (GAA) formal name is Boulder Opal, with a Queensland designation note. Institution usageOn authority wording, among GIA, FTC, CIBJO and Gem-A, CIBJO lists Boulder Opal (CIBJO Gemmological Laboratories Book 2024); the FTC text has no wording for this name (checked); GIA and Gem-A have not been checked. The English name shown for bodies without a recorded wording comes from the Boulder Opal entry and does not represent their position.

Authority wording

GIA, FTC, CIBJO, Gem-A
Boulder Opal (on record for CIBJO (CIBJO Gemmological Laboratories Book 2024); no wording for this name in the FTC text on file; GIA, Gem-A unchecked — bodies without a recorded wording show the entry's own English name)
GSJ (Japan) formal name
ボルダーオパール (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)
欧泊 (GB/T 16552—2017 Table A.2)
Mineralogical name
Thin natural opal layer on ironstone or sandstone host rock

Four-language names

简体中文
砾背欧泊
繁體中文
礫背歐泊
English
Boulder Opal
日本語
ボルダーオパール

National and regional formal names

Australia (GAA)
Boulder Opal; Queensland designation

See also: Misleading and prohibited trade names · Supplementary name index

Classification

Origin
Natural materials
Material domain
Natural inorganic gem materials
Browsing family
Opal and natural amorphous silica materials
Identity tier
Mineral / gemstone variety
Mineral chemical class
Not applicable
Construction or treatment status
Natural identity; treatment status unknown

Treatments listed by standards

GB/T Table B.1For Boulder Opal, this site applies the “Opal” row of GB/T 16552—2017 Annex B, Table B.1: filling is listed by the standard's grades, and dyeing and coating are both listed as treatment. What Table B.1 notes and how the grades are defined are explained on the Gem treatments page. JJA/AGL designationsIn the “principal gem designations” table of the Japanese JJA/AGL “Definitions and Nomenclature of Gemstones and Ornamental Materials”, revised November 2025, Boulder Opal is listed under the species name opal, with whether a treatment category applies noted, and filling of the host rock (filling treatment) listed, with the note that it shows play-of-colour and has a limonite host rock; how to read the JJA/AGL table is explained on the Gem treatments page.

GB/T 16552-2017, Annex B, Table B.1

Under the “Opal” row of Table B.1: Filling Graded — see §5.4.1, Table 1; Dyeing Treatment; Coating Treatment. The full row, with the effect column, is on the Opal page.

What Table B.1 is, and how the “see 5.4.1” grades are defined: see the GB/T 16552: optimization vs treatment page.

JJA/AGL (Japan) table of principal gem names, 2025

This table scrolls sideways on narrow screens.

Gem nameSpeciesColourListed in the tableNotes
Boulder OpalOpalan untreated tier is listed; filling of the host rock (Filled / Fracture-filled)play of colour; with ironstone host rock

JJA/AGL definitions and nomenclature (2025 revision), table of principal gem names, p.9

How to read the JJA/AGL table: see the Gem treatments page.

What it is and how it's identified

Boulder Opal is composed of opal (phase). Recorded for opal (the whole class): structure (overall) amorphous; cleavage none; density 1.25–2.23 g/cm³ (the cited clause value is 2.15 with tolerance +0.08/-0.90, from which the limits are derived); refractive index 1.37–1.47 (the cited clause value is 1.450 with tolerance +0.020/-0.080, from which the limits are derived; the clause has finer ranges and the overall value is used); birefringence none; optic character isotropic, with anomalous extinction often seen in fire opal; play-of-colour may be seen; and, as a quality factor for untreated material, vitreous to resinous lustre. Mohs hardness is 5–6.5; the cited clause covers the whole species, of which Boulder Opal is only one variety.

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 opal (whole class), so they are not repeated on the Boulder Opal page; see the material facts on the Opal entry.

Items below that name the class they cover give the cited clause’s value for that whole class, not a measurement of Boulder Opal (how to read class-level values).

Definition

Boulder Opal — composition (phase): opal

CIBJO Gemmological Laboratories Book 2024

Source & check 2026-09-22
Source
Fact checked on
2026-09-22

Structure

Boulder Opal — structure (overall): amorphous (not crystalline)

GB/T 16553—2017

Does this standard apply
applies to this entry
What this covers
opal (whole class)
Source & check 2026-09-26
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
Fact checked on
2026-09-26

Durability

Boulder Opal — Mohs hardness: 5–6.5

GIA Opal

123456789105–6.5References (diamond = value, bar = range; below)

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))

Mohs hardnessSource: GIA Opal
Qualification

The clause we cite covers the whole species. This entry is only one variety of it.

Source & check 2026-09-20
Source
Fact checked on
2026-09-20

Boulder Opal — cleavage: none

GB/T 16553—2017

Does this standard apply
applies to this entry
What this covers
opal (whole class)
Source & check 2026-09-26
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
Fact checked on
2026-09-26

Boulder Opal — stability: chips and cracks easily; porous, so keep it away from coloured liquids; will craze if it loses water, so keep it away from heat and dry air; avoid sudden temperature changes; no ultrasonic cleaning.

CIBJO Gemstone Book 2022

CIBJO Gemstone Book §6.2:special-care code b, special-care code c, special-care code d, special-care code e, special-care code j

Treatment state
untreated
Source & check 2026-09-21
Source
Fact checked on
2026-09-21

Physical properties

Boulder Opal — density: 1.25–2.23 g/cm³

GB/T 16553—2017

0.51.52.53.54.55.56.57.51.25–2.23
Specific gravitySource: GB/T 16553—2017
Does this standard apply
applies to this entry
What this covers
opal (whole class)
Qualification

The clause we cite gives 2.15, with a stated tolerance of +0.08 / -0.90. The range shown here is worked out from that.

Source & check 2026-09-21
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-21)
Fact checked on
2026-09-21

Optical

Optical effects on record: play of colourrepresentative example: cause in Opal (schematic)chatoyancyrepresentative example: cause in Tiger’s Eye (schematic)

Boulder Opal — optic character: isotropic; fire opal commonly shows anomalous extinction.

GB/T 16553—2017

Does this standard apply
applies to this entry
What this covers
opal (whole class)
Source & check 2026-09-26
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
Fact checked on
2026-09-26

Boulder Opal — refractive index: 1.37–1.47

GB/T 16553—2017

1.31.72.12.52.93.31.37–1.47
Refractive indexSource: GB/T 16553—2017
Does this standard apply
applies to this entry
What this covers
opal (whole class)
Qualification

The clause we cite gives 1.450, with a stated tolerance of +0.020 / -0.080. The range shown here is worked out from that.

General note
the clause has finer ranges
Source & check 2026-09-21
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-21)
Fact checked on
2026-09-21

Boulder Opal — birefringence: none

GB/T 16553—2017

Does this standard apply
applies to this entry
What this covers
opal (whole class)
Source & check 2026-09-21
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-21)
Fact checked on
2026-09-21

Boulder Opal — pleochroism: none

GB/T 16553—2017

Treatment state
untreated
Does this standard apply
applies to this entry
What this covers
opal (whole class)
Source & check 2026-09-26
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
Fact checked on
2026-09-26

optical effect (play of colour)2 sources compared

Boulder Opal — optical effect (play of colour): seen

GB/T 16553—2017

Does this standard apply
applies to this entry
What this covers
opal (whole class)
Source & check 2026-09-26
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
Fact checked on
2026-09-26

Boulder Opal — optical effect (play of colour): play-of-colour.

CIBJO Gemmological Laboratories Book 2024

Source & check 2026-09-22
Source
Fact checked on
2026-09-22

Boulder Opal — optical effect (chatoyancy): seen; rare

GB/T 16553—2017

Does this standard apply
applies to this entry
What this covers
opal (whole class)
Source & check 2026-09-26
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
Fact checked on
2026-09-26
CIBJO definitions
play of colour, chatoyancy

Quality factors

Boulder Opal — quality factor (lustre): vitreous to resinous

GB/T 16553—2017

Treatment state
untreated
Does this standard apply
applies to this entry
What this covers
opal (whole class)
Source & check 2026-09-26
Source
  • GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
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.

1.451.51.822.2Refractive indexSpecific gravity12345Boulder Opal

This material (RI / SG midpoints): 1.42 / 1.74; Closest values: 1Synthetic Opal 1.45 / 2.08, 2Mammoth Ivory 1.53 / 1.75, 3Ivory 1.535 / 1.85, 4Hackmanite 1.483 / 2.27, 5Chrysocolla 1.516 / 2.2

Show the full chart (330 registered materials)1.41.51.61.71.81.922.12.22.32.41234567Refractive indexSpecific gravity12345Boulder Opal

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

Refractive index × specific gravity (all registered materials)Each dot is one material's registered refractive index and specific gravity (range midpoints, not measurements); gold = this material, dark = the nearest few (picked on this site by distance in RI ÷ 0.02 and SG ÷ 0.1, leaving out near-identical varieties of the same species)Source: each material's registered refractive index and specific gravity facts (GB/T 16553 and others; sources on each entry)

Testing and market

The CIBJO laboratory protocol covers Boulder Opal under “Opal” (§6.1.56): see identification on the Opal entry; the required tests are listed on the CIBJO laboratory protocol table for Opal.

How far testing can go

Each row's “Source & check” expands to the full source; the date beside it is the fact check date.

Clause-level definitions

Boulder Opal is defined directly in the Boulder opal entry of the CIBJO Gemmological Laboratories Book 2024. The summary definition states that the mineral species is opal, the host rock is ironstone or sandstone, and the trade name is boulder opal; the CIBJO wording is quoted in full under Clause-level definitions on this page. Cross-check result: defined directly by CIBJO; the same English name was not found directly in the GB/T annex of this edition.

This table scrolls sideways on narrow screens.

TermClauseDefinitionCross-check
Boulder opal7.2.1.32Thin seam of opal with play-of-colour occurring in a host rock matrix (ironstone or sandstone)Defined directly by CIBJO; no identically named English entry was found in this edition of the GB/T annex.

Evidence and sources

Authority basis and clause sources

GB/T 16552—2017
Not listed the name does not occur anywhere in the text; scope: Chapter 1 “Scope” · Source
IMA Mineral List 2026-07
Listed “Opal” · Source
CIBJO Gemmological Laboratories Book 2024
Listed §7.2.1.32 “Boulder opal” · Source

Sources

Further reading

Related pages

Treatments recorded for this material

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 Opal on this site: 17 entries listed by this site's parent-entry links; synthetic, treated and similar entries carry their recorded state after the name; this page (Boulder Opal) is marked.

This table scrolls sideways on narrow screens.

PageContentStatus
Browsing familyOpal and natural amorphous silica materialsLive
Treatments recorded for this materialFilled / Fracture-filled, Dyed (via parent material), Coated (via parent material)Live
Related articlesTo be added (placeholder)Planned

Who maintains this page

The material facts in the Boulder Opal 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; clause-level definitions also carry a cross-check result. The entry exists so that buyers and sellers can check naming, disclosure and material facts item by item.

Facts editor
Ralph
Reviewer
June
How facts are checked
Each fact is matched to the clause it cites; facts checked between 2026-09-20 and 2026-09-26
Last revised
2026-10-12
Purpose
Lets buyers and sellers check naming, disclosure and material facts clause by clause.

Spotted an error? Report it on the forum