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Natural organic and biogenic materials · Organic or biogenic material · Natural identity; treatment status unknown
Giant Clam Shell
Also known asTridacna shell
Shell material from large clams of the giant clam family; the entire family TRIDACNIDAE is listed in CITES Appendix II, so international trade requires a permit. 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 Giant Clam Shell forms and what gives its colourFormation setting, process and timescale, each finding graded and sourced
- How to identify Giant Clam ShellIdentification points from the research literature; how far lab testing can go
- Treatments and enhancements of Giant Clam ShellThe enhancements and treatments the GB/T and JJA/AGL tables list
- Hardness, density and refractive index of Giant Clam ShellEach value with its source and check date
- Giant Clam Shell in English, Chinese and Japanese; national standard namesNames in four languages, the GB/T standard name and the suggested listing name; and: Has any of GIA, FTC, CIBJO or Gem-A put a name for it on record here?
- Listing and disclosing Giant Clam ShellThe 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
Tridacna is shell material from giant clams of the family Tridacnidae, a biogenic calcium-carbonate material. Living clams inhabit warm marine waters of the Indo-Pacific; here the mantle secretes aragonite (calcium carbonate) which accumulates in layers, building heavy, fluted shells; the interior is white to cream with a porcelaneous, porcelain-like surface and often displays flame structure. Fossil Tridacna shells are found in raised reef deposits, and their aragonite can be replaced by calcite through diagenesis/fossilisation. Every species of the family Tridacnidae is currently listed in CITES Appendix II, so international trade is regulated.
Scope: Covers the biogenic origin, environment of occurrence and CITES Appendix listing of giant clam shell material; not to be used for assessments of species, farmed/wild provenance or treatment of specific samples.
Sources G&G Spring 2015 · CITES Checklist · G&G Summer 2017
Where it forms
Warm shallow Indo-Pacific coral-reef waters where giant clams grow and secrete their shells.
Sources G&G Spring 2015
Fossil Tridacna shells occur in raised coral reefs and secondary fossil reef build-up (e.g. along the Kenyan coast).
Sources G&G Winter 2015
How it forms, step by step
The clam grows in warm seas, its mantle secreting calcium carbonate (aragonite) that builds in layers into a heavy shell.
The shell is heavy and multiply fluted, its interior white to cream with a porcelain-like surface and common flame structure.
Fossil shells are preserved in raised-reef deposits, where aragonite may be replaced by calcite during fossilisation.
The shell, once harvested, is fashioned into beads, ornaments or imitation-pearl material.
Link to appearance
The porcelain-like interior and flame structure reflect the aragonitic, non-nacreous shell structure; the heavy, fluted shape reflects growth in the reef environment.
Sources G&G Spring 2015 · G&G Summer 2017
Timescale
The cited sources give no absolute timescale for Tridacna shell growth or fossilisation; fossil shells are dated only relatively by strata (e.g. later Pleistocene).
Sources G&G Winter 2015
Supporting findings
Tridacna is the shell material of giant clams of the family Tridacnidae and is a biogenic calcium-carbonate material.
Evidence grade AScope: Material-category level; not for identifying a specimen's species or source.
Recorded localities
This is an organic material; its localities are the harvest or culture areas (waters or species ranges) recorded by authoritative sources.
Africa
- Kenyan coastFossil giant clam shells (raised coral reef)
Seas and coasts
- Warm waters of the Indo-PacificNatural habitat; the family is listed in CITES Appendix II
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.
How it is identified
Giant-clam shell (tridacna) is not identified by its creamy look, which imitations and dyed or treated material can match. Its calcium-carbonate skeleton and internal structure must be assessed with instruments; separating natural shell from imitations and spotting treatments requires a qualified gem laboratory, and this entry is no basis for self-testing.
Evidence grade AScope: Applies to giant-clam shell; identification and any treatment call require testing at a qualified gem laboratory.
Sources CIBJO Coral Blue Book 2024
Other research findings
All species of the family Tridacnidae are listed in CITES Appendix II, with Tridacna gigas more vulnerable than Tridacna squamosa or Tridacna maxima.
Evidence grade AScope: Current CITES Appendix-level status (updated at Conferences of the Parties). 'Protected' does not mean a total trade ban; under Appendix II trade requires permits and evidence of legal origin.
The CITES Checklist lists Tridacna gigas in CITES Appendix II, under the family listing Tridacnidae spp. effective 01/08/1985.
Evidence grade AScope: Current Appendix-level status, updated at CoPs; not a substitute for permit/customs verification.
The CITES Checklist lists Tridacna maxima in CITES Appendix II, likewise under the family listing Tridacnidae spp. effective 01/08/1985.
Evidence grade AScope: Current Appendix-level status, updated at CoPs; not case-specific verification.
Giant clams are commonly harvested for food from natural habitats or aquaculture farms, and their shells are fashioned into beads or ornaments; shell and pearls are porcelaneous and non-nacreous.
Evidence grade AScope: Describes use and material structure; does not establish the legal origin of any product.
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 Tridacna shell growth or fossilisation.
- A specimen's species, farmed/wild source and treatment cannot be determined from these sources.
- CITES Appendix levels are current status and are updated at Conferences of the Parties.
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
- Giant clam shell (subject to trade-compliance clearance)
GB/T 16552—2017 Table A.3 “Shell” · CITES Appendices 2026 “TRIDACNIDAE”
Construction or treatment status
Natural identity; treatment status unknown
Treatments recorded for this material: Coated (via parent material), Dyed (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
"Giant Clam Shell" is a market name rather than a mineral species name; before using it, verify: Compliance review required before listing.
What this means for you
Before buying, check the recommended listing name "Giant clam shell (subject to trade-compliance clearance)" 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
- 2026-09-01
Trade-name ruling
- Compliance review required before listing.
- Suggested listing name
- Giant clam shell (subject to trade-compliance clearance)
Care and wear
No care facts are recorded for this entry itself. Its parent material has care records: see Shell.
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.
| Treatment | Market frequency (CIBJO) | Stability (CIBJO) | GB/T 16552 category | JJA/AGL listing | Identification leads |
|---|---|---|---|---|---|
| Coating | — | — | Graded — see §5.4.1, Table 1 | — | — |
| Dyeing | — | — | Treatment | — | — |
“—” means the cited source gives no value for that item, not “none”. Source: GB/T 16552—2017 Table B.1 (row for Shell)
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
Besides Giant Clam Shell, the name register records "Tridacna shell", for which no restriction on use as a name is recorded (CITES Appendices 2026 TRIDACNIDAE; CITES Convention text Article IV(2)).
Name register
Every name recorded for this entry, with how it is classified, whether it may be matched to this entry automatically, whether it may be used as a product name, and the clause it rests on.
This table scrolls sideways on narrow screens.
| Name | Type | Matching | Use as a name | Basis |
|---|---|---|---|---|
| no restriction recorded (1) | ||||
| Tridacna shellEnglish | market name | matched automatically | no restriction recorded | CITES Appendices 2026 TRIDACNIDAE; CITES Convention text Article IV(2); Note: Related high-risk name “Coral, giant clam shell”: CITES and import rules apply — the whole family TRIDACNIDAE spp. is listed in Appendix II, and export needs a prior export permit (Convention Article IV(2)). |
How each authority words this name: see Names › Authority wording.
- GSJ (Japan) formal name
- シャコガイ (not yet checked for this body — the entry's own Japanese name is shown)
- Chinese formal name
- 砗磲 (GB/T 16552—2017 Table A.3)
- Mineralogical name
- Shell material from giant clams
- Trade names and synonyms
- Tridacna shell (market name)
Four-language names
- 简体中文
- 砗磲
- 繁體中文
- 硨磲
- English
- Giant Clam Shell
- 日本語
- シャコガイ
See also: Misleading and prohibited trade names · Supplementary name index
Classification
- Origin
- Natural materials
- Material domain
- Natural organic and biogenic materials
- Browsing family
- Pearl and molluscan shell materials
- Identity tier
- Organic or biogenic material
- Mineral chemical class
- Not applicable
- Construction or treatment status
- Natural identity; treatment status unknown
Treatments listed by standards
The treatment items for Giant Clam Shell are applied by this site from the “Shell” row of GB/T 16552—2017 Annex B, Table B.1, as GB/T 16552—2017 itself has no separate treatment row for giant clam shell: coating is classed according to its grades, and dyeing is classed as treatment. The effects of coating and dyeing are described on the Shell entry, and what Table B.1 notes and how each grade is defined are explained on the Gem treatments page.
GB/T 16552-2017, Annex B, Table B.1
Under the “Shell” row of Table B.1: Coating Graded — see §5.4.1, Table 1; Dyeing Treatment. The full row, with the effect column, is on the Shell 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.
What it is and how it's identified
Most of the registered material facts for Giant Clam Shell state that the cited clause is written for shell as a whole class, not measured for Giant Clam Shell alone. For shell as a whole class: the inorganic part is a radially arranged aggregate, with aragonite orthorhombic and calcite trigonal, and the organic part amorphous; cleavage is usually not seen in aggregates; Mohs hardness is 3–4, a range for the whole class, not a measurement of Giant Clam Shell alone. Density of 2.7–2.89 g/cm³ is likewise taken for shell as a whole class: the cited clause gives 2.86 with a tolerance of +0.03/−0.16, from which these limits are derived. The optical properties are also for shell as a whole class: optical character is aggregate, and the refractive index of 1.53–1.68 is the range commonly obtained by the spot method, a typical value rather than an absolute limit. Untreated, pleochroism cannot be measured because it is an aggregate, and an optical effect (iridescence) may be seen; untreated, the lustre is greasy to pearly, and it effervesces with a drop of hydrochloric acid.
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”.
Luminescence, UV-visible spectrum, infrared spectrum, magnification: these whole-class features are given in the cited clause for shell (whole class), so they are not repeated on the Giant Clam Shell page; see the material facts on the Shell entry.
Items below that name the class they cover give the cited clause’s value for that whole class, not a measurement of Giant Clam Shell (how to read class-level values).
Structure
Giant Clam Shell — structure (overall): inorganic part: radiating aggregates of aragonite (orthorhombic) and calcite (trigonal); organic part: amorphous.
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- shell (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Durability
Giant Clam Shell — Mohs hardness: 3–4
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
- shell (whole class)
- Qualification
This is the range for the whole class, not a measured value for this variety. The clause covers all shell.
Source & check 2026-09-20
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-20)
- Fact checked on
- 2026-09-20
Giant Clam Shell — cleavage: generally not seen on an aggregate
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- shell (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Giant Clam Shell — stability: effervesces on contact with hydrochloric acid
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- shell (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Physical properties
Giant Clam Shell — density: 2.7–2.89 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- shell (whole class)
- Qualification
The clause we cite gives 2.86, with a stated tolerance of +0.03 / -0.16. The range shown here is worked out from that.
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Optical
Giant Clam Shell — optic character: aggregate
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- shell (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Giant Clam Shell — refractive index: 1.53–1.68
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- shell (whole class)
- Qualification
The clause we cite gives this as a value commonly read by the spot (distant-vision) method. It is a common value, not an absolute limit.
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Giant Clam Shell — pleochroism: not measurable on an aggregate
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- shell (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Giant Clam Shell — optical effect (iridescence): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- shell (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Quality factors
Giant Clam Shell — quality factor (lustre): greasy to pearly
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- shell (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (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.
This material (RI / SG midpoints): 1.605 / 2.79; Closest values: 1Saltwater Natural Pearl 1.605 / 2.73, 2Natural Conch Pearl / Natural Melo Pearl 1.595 / 2.84, 3Larimar 1.62 / 2.82, 4Muscovite 1.58 / 2.8, 5Prehnite 1.625 / 2.88
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
Pearl-producing molluscs (CIBJO Annex D)
Pearl-producing molluscs (CIBJO Annex D): §9.25 Giant Clam · §9.29 Hippopus spp. · §9.82 Tridacna gigas
Testing and market
The CIBJO laboratory protocol covers Giant Clam Shell under “Pearl” (§6.2.25): see identification on the Pearl entry; the required tests are listed on the CIBJO laboratory protocol table for Pearl.
How far testing can go
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.
- CIBJO – The World Jewellery Confederation. The Pearl Book (Blue Book), 2024.
- CITES Secretariat. Appendices I, II and III, valid from 5 March 2026.
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 Shell 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 (Giant Clam Shell) is marked.
- Shell
Sub-entries (2)
- Giant Clam Shell
- Mother-of-Pearl / Nacre
This table scrolls sideways on narrow screens.
| Page | Content | Status |
|---|---|---|
| Browsing family | Pearl and molluscan shell materials | Live |
| Treatments recorded for this material | Coated (via parent material), Dyed (via parent material) | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Giant Clam Shell 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.