On this page
UnderstandWhat it is, what people ask, how far this page goes
Natural organic and biogenic materials · Organic or biogenic material · Natural identity; treatment status unknown
Shell
Also known asConch Shell · Pink Conch
Shell material from molluscs, listed as “shell” in Table A.3 of GB/T Annex A; when used, the species and the shell layer taken must be stated. 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 Shell forms and what gives its colourFormation setting, process and timescale, each finding graded and sourced
- How to identify ShellIdentification points from the research literature; how far lab testing can go and whether a synthetic exists
- Treatments and enhancements of Shell2 registered treatments: status, stability, how common they are and identification leads
- Caring for and wearing ShellCleaning, heat, chemicals and light, as the cited sources give them; durability indicators and wearing advice
- Hardness, density and refractive index of ShellEach value with its source and check date
- Shell in English, Chinese and Japanese; national standard namesNames in four languages, the GB/T standard name and the suggested listing name, names in national standards; and: Which of GIA, FTC, CIBJO and Gem-A have a name for it on record, and do those agree?
- Name origin and history of ShellWhere the name comes from; how people have used it, with museum objects
- Listing and disclosing ShellThe listing name to use; what must be disclosed before sale
- Standard clauses that define ShellWhich clause defines it, each cross-checked
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
Shell is a hard material built by molluscs through biomineralization. Using organic matrix secreted by the mantle as a template, and within a highly structured chitinous framework, molluscs crystallize calcium carbonate from a hydrophobic silk gel, acidic aspartate-rich proteins and an amorphous precursor phase, building layered structures such as nacre. Shell is generally an alternation of aragonite (occasionally calcite) with organic matrix; as an aggregate material its composition varies with species and with the shell layer.
Scope: Applies to an overview of the formation and composition of mollusc shells (biomineralised composite materials); specific species and shell layers must each be indicated where involved.
Sources Journal article (mollusk shell formation) · G&G Fall 2021 · Handbook of Mineralogy +2
- Mollusk Shell Formation: A Source of New Concepts for Understanding Biomineralization Processes
- Internal Structures of Known Pinctada maxima Pearls: Cultured Pearls from Operated Marine Mollusks (Gems & Gemology, Fall 2021, Vol. 57, No. 3)
- Handbook of Mineralogy — Aragonite (CaCO3)
- Checklist of CITES Species (checklist.cites.org), consulted 2026-10-03 and re-checked 2026-10-05
- Hyperspectral interference tomography of nacre
Where it forms
The mollusc mantle tissue and mantle cavity — where shell and pearl are secreted.
Sources Journal article (mollusk shell formation) · Handbook of Mineralogy
After death, shells can also be buried as a component of warm marine sediment.
Sources Journal article (mollusk shell formation) · Handbook of Mineralogy
How it forms, step by step
Mantle epithelial cells secrete an organic matrix (proteins and polysaccharides), building a chitinous framework as the mineralisation template.
Sources Journal article (mollusk shell formation) · Handbook of Mineralogy
On the matrix template, calcium carbonate (typically aragonite) crystallizes from an amorphous precursor phase.
Sources Journal article (mollusk shell formation) · Handbook of Mineralogy
Calcium carbonate in a brick-type arrangement of aragonite tablets alternates with organic matrix, forming layered structures such as nacre.
Sources Journal article (mollusk shell formation) · Handbook of Mineralogy
Different species and shell layers may be dominated by aragonite or calcite, so that composition and structure differ by layer.
Sources Journal article (mollusk shell formation) · Handbook of Mineralogy
Link to appearance
The pearly lustre of shell (nacre iridescence) arises from interference at the alternating aragonite tablet/organic-matrix layering; layer and species determine the appearance.
Sources G&G Fall 2021 · CITES Checklist
Timescale
No authoritative shell growth-rate figure is given here, though aragonite tablet thickness in nacre is used as a proxy for mollusc age.
Sources Journal article (mollusk shell formation) · Handbook of Mineralogy
Related base materials
- Aragonite: Main inorganic phase (a calcium carbonate polymorph)
Supporting findings
In building their shells, molluscs deploy a hydrophobic silk gel, proteins that are acidic and rich in aspartate, and an amorphous precursor phase as well; the whole process unfolds inside a chitinous framework of highly structured form.
Evidence grade AScope: Describes the biomineralization mechanism of molluscan shell; not specific to one species.
Sources Journal article (mollusk shell formation)
Aragonite serves as one of the main detrital sedimentary constituents, making up the hard parts — shells and skeletons — of numerous marine micro-organisms.
Evidence grade BScope: States the sedimentary occurrence of aragonite; not exclusive to shell.
Sources Handbook of Mineralogy
Where the name comes from
The cited source gives no etymology for the name shell; the etymology cited belongs to its principal inorganic phase, aragonite, which is named for its earliest recorded find in the Aragon region, Spain.
Evidence grade BScope: The etymology explains the origin of a name only; it does not attest composition, locality, naturalness or treatment, and here belongs to the parent mineral rather than to the trade name itself.
Sources Handbook of Mineralogy
Human use and museum objects
Earlier shell ornaments include The Met 16.7.54 "shell pendant or bead" (ca. 3850–2960 BCE, Egypt, Predynastic Period) and 09.180.1200 "cowrie shell bead" (ca. 1850–1640 BCE, gold, Memphite Region); shell was used as a body ornament in the Nile Valley from the Neolithic to the Bronze Age.
Evidence grade AScope: Catalogue objects attest only to the existence and dating of those individual pieces; they are not evidence that the material was in common use in antiquity, nor do they attest to the origin, naturalness or treatment of any modern sample. Cultural attributions follow the museum's records and are not extended.
Sources The Met 16.7.54 · The Met 09.180.1200 · Cleveland Museum of Art 1946.230 +2
Shell ornaments also occur in the Americas and Africa: Cleveland 1946.230 (c. 900–600 BCE, north coast of Peru, Cupisnique style, bird ornament of shell with stone inlay), 1955.178 (50–800 CE, Moche, frog ornament) and 1994.87 (possibly early 1900s, DR Congo, Kuba style, royal belt with shells and cowrie shells). Cultural attributions follow the museum's records and are not extended.
Evidence grade AScope: Catalogue objects attest only to the existence and dating of those individual pieces; they are not evidence that the material was in common use in antiquity, nor do they attest to the origin, naturalness or treatment of any modern sample. Cultural attributions follow the museum's records and are not extended.
Sources The Met 16.7.54 · The Met 09.180.1200 · Cleveland Museum of Art 1946.230 +2
Shell as a body ornament has early catalogue evidence: The Met 16.7.54 (shell pendant or bead, ca. 3850–2960 BCE, Egypt, Predynastic Period) and 09.180.1200 (cowrie shell bead, ca. 1850–1640 BCE, gold, Memphite Region) show its use in the Nile Valley from the Neolithic to the Bronze Age. Shell ornaments also occur in the Americas and Africa: Cleveland 1946.230 (bird ornament, c. 900–600 BCE, north coast of Peru, Cupisnique style, shell with stone inlay), 1955.178 (frog ornament, 50–800 CE, Moche, shell, stone and gold) and 1994.87 (royal belt yet, possibly early 1900s, DR Congo, Kuba style, with shells and cowrie shells).
Sources The Met 16.7.54 · The Met 09.180.1200 · Cleveland Museum of Art 1946.230 +2
Scope: Catalogue objects attest only to the existence and dating of those individual pieces; they are not evidence that the material was in common use in antiquity, nor do they attest to the origin, naturalness or treatment of any modern sample. Cultural attributions follow the museum's records and are not extended.
Objects cited
- The Met 16.7.54Shell
- The Met 09.180.1200Gold
- Cleveland Museum of Art 1946.230shell with stone inlay
- Cleveland Museum of Art 1955.178shell, stone, gold
- Cleveland Museum of Art 1994.87Plant fiber, rawhide or leather, glass beads, seashells, cowrie shells, cloth, and colorant
How it is identified
Shell resembles imitation or treated shell material in appearance, and looks alone struggle to establish its kind or treatment status. Identification requires laboratory testing of structure and composition with instruments; the conclusion should be issued by an accredited body, and no do-it-yourself criteria are offered here.
Evidence grade AScope: Shell identification requires an accredited laboratory; no self-identification basis is provided.
Sources CIBJO Gemstone Book 2022
Other research findings
Nacre in a shell is built from calcium carbonate — specifically the aragonite polymorph — laid out in a brick-type arrangement, plus an organic matrix made of proteins and polysaccharides; the combination is what bears the name nacre.
Evidence grade AScope: Applies to nacre; other shell layers (e.g. prismatic) differ in composition.
As an aggregate material, shell requires the species and layer to be specified; some shells (e.g. Tridacna) are listed in CITES Appendix II, so legality depends on species and permits.
Evidence grade AScope: Defines naming boundary and trade control; no judgement on source legality.
Aragonite tablets in nacre grow thicker or thinner according to the mollusc's age, and this thickness serves as a proxy both for the mollusc's age and for the temperature of ancient seawater.
Evidence grade AScope: An applied finding about nacre structure; does not alter the genesis conclusion.
Sources Journal article (nacre tomography)
Limits of this research
- Research status: Formation, occurrence or other material-specific findings found in authoritative sources
- Shell is an aggregate material whose composition varies by species and layer; only a general overview is given.
- Some shell species are CITES-controlled (e.g. Tridacna, Appendix II); legality depends on species and permits and is not adjudicated here.
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
- Shell (state the species, part and any treatments)
GB/T 16552—2017 Table A.3 “Shell” · CIBJO Gemmological Laboratories Book 2024 §7.2.2.10 “Shell”
Construction or treatment status
Natural identity; treatment status unknown
Treatments recorded for this material: Coated, Dyed
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
"Shell" is a market name rather than a mineral species name; before using it, verify: Industry-wide term that does not denote a single species.
Evidence
- GB/T · Table A.3, row 贝壳 (Shell)
What this means for you
Before buying, check the recommended listing name "Shell (state the species, part and any treatments)" 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
- Industry-wide term that does not denote a single species.
- Suggested listing name
- Shell (state the species, part and any treatments)
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.
Care
care (cleaning)2 sources compared
Shell — care (cleaning): Some stones are susceptible to damage from ultrasonic cleaning. Do not expose them to ultrasonic cleaning.
CIBJO Gemstone Book 2022
CIBJO Gemstone Book §6.2:special-care code j
- Treatment state
- any treatment state
Source & check 2026-09-25
- Source
- CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §8 Annex C, Shell, p.76; §6.2 j (locator checked 2026-09-25)
- Fact checked on
- 2026-09-25
Shell — care (cleaning): ultrasonic and steamer: use caution.
Gems & Gemology 1987 (Martin)
- Treatment state
- untreated
Source & check 2026-09-26
- Source
- Martin, “Gemstone Durability: Design to Display”, Gems & Gemology, Summer 1987: pp.66–67 fold-out chart, Shell row, CLEANING column (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Shell — care (light): may fade or revert to its original colour in strong light; do not wear or leave it in strong light for extended periods.
CIBJO Gemstone Book 2022
CIBJO Gemstone Book §6.2:special-care code f
- Treatment state
- any treatment state
Source & check 2026-09-25
- Source
- CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §8 Annex C, Shell, p.76; §6.2 f (locator checked 2026-09-25)
- Fact checked on
- 2026-09-25
Shell — 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
- dyeing
Source & check 2026-09-25
- Source
- CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §8 Annex C, Shell, p.76; §6.2 k (locator checked 2026-09-25)
- Fact checked on
- 2026-09-25
Shell — care (chemicals): porous, so do not let it come into contact with coloured fluids; particularly susceptible to attack by acids, so keep it away from acids.
CIBJO Gemstone Book 2022
CIBJO Gemstone Book §6.2:special-care code c, special-care code h
- Treatment state
- any treatment state
Source & check 2026-09-25
- Source
- CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §8 Annex C, Shell, p.76; §6.2 c, h (locator checked 2026-09-25)
- Fact checked on
- 2026-09-25
Shell — care (wear): Some stones are prone to scratching due to low hardness. Wear them with care.
CIBJO Gemstone Book 2022
CIBJO Gemstone Book §6.2:special-care code a
- Treatment state
- any treatment state
Source & check 2026-09-25
- Source
- CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §8 Annex C, Shell, p.76; §6.2 a (locator checked 2026-09-25)
- Fact checked on
- 2026-09-25
Shell — care (setting): prong, bezel and channel: use caution; flush and pavé: avoid.
Gems & Gemology 1987 (Martin)
- Treatment state
- untreated
Source & check 2026-09-26
- Source
- Martin, “Gemstone Durability: Design to Display”, Gems & Gemology, Summer 1987: pp.66–67 fold-out chart, Shell row, SETTING column (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Shell — care (repair): polishing: use extreme caution; jeweller's torch, pickle pot and thermal shock: avoid; note: avoid heat, as it blackens in flame; avoid acids.
Gems & Gemology 1987 (Martin)
- Treatment state
- untreated
Source & check 2026-09-26
- Source
- Martin, “Gemstone Durability: Design to Display”, Gems & Gemology, Summer 1987: pp.66–67 fold-out chart, Shell row, REPAIR column (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Shell — care (display): Dyed material may fade
Gems & Gemology 1987 (Martin)
- Treatment state
- treated
- Only after these treatments
- dyeing
Source & check 2026-09-26
- Source
- Martin, “Gemstone Durability: Design to Display”, Gems & Gemology, Summer 1987: pp.66–67 fold-out chart, Shell row, DISPLAY column (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Shell — care (display): heat in the display case, sunlight and artificial light: use caution.
Gems & Gemology 1987 (Martin)
- Treatment state
- untreated
Source & check 2026-09-26
- Source
- Martin, “Gemstone Durability: Design to Display”, Gems & Gemology, Summer 1987: pp.66–67 fold-out chart, Shell row, DISPLAY column (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.
Common care questions and matching entries
CleaningOn cleaning Shell, CIBJO states that, regardless of treatment status, shell must not be cleaned ultrasonically; Martin's Gemstone Durability: Design to Display states that for untreated shell, ultrasonic and steam cleaning call for caution. CIBJOCIBJO also states that, regardless of treatment status, shell is porous, so keep it away from coloured liquids, and it is particularly sensitive to acids, so keep it away from acids; it may fade or revert to its original colour in strong light, so do not wear or keep it in strong light for long periods; it is soft and scratches easily, so wear it with care; for shell whose status is treated, and only where dyed, treatments with dye, oil, resin, wax or plastic are not permanent, so keep it away from all solvents (including dish-washing liquids), chemicals and heat. Martin, Gem DurabilityMartin's Gemstone Durability: Design to Display also states that for untreated shell, prong, bezel and channel settings call for caution, and tension and pavé settings should be avoided; polishing calls for particular caution, and the jeweller's torch, post-soldering pickling solution and thermal shock should be avoided; avoid heat, as it blackens in flame, and avoid acids; heat, daylight and artificial light in display cases call for caution; for shell whose status is treated, and only where dyed, dyed shell may fade.
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| Question | Matching entries |
|---|---|
| Can it go in an ultrasonic or steam cleaner? | care (cleaning); ultrasonic and steamer: use caution |
| Heat and thermal shock | polishing: use extreme caution; jeweller's torch, pickle pot and thermal shock: avoid; note: avoid heat, as it blackens in flame; avoid acids |
| Light and display | may fade or revert to its original colour in strong light; do not wear or leave it in strong light for extended periods; Dyed material may fade; heat in the display case, sunlight and artificial light: use caution |
| Contact with acids, alkalis and household 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; porous, so do not let it come into contact with coloured fluids; particularly susceptible to attack by acids, so keep it away from acids |
| Wearing limits (knocks, settings) | care (wear); prong, bezel and channel: use caution; flush and pavé: avoid |
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.
any treatment state
- care (cleaning) §6.2 j
- may fade or revert to its original colour in strong light; do not wear or leave it in strong light for extended periods §6.2 f
- porous, so do not let it come into contact with coloured fluids; particularly susceptible to attack by acids, so keep it away from acids §6.2 c, h
- care (wear) §6.2 a
untreated
- ultrasonic and steamer: use caution
- prong, bezel and channel: use caution; flush and pavé: avoid
- polishing: use extreme caution; jeweller's torch, pickle pot and thermal shock: avoid; note: avoid heat, as it blackens in flame; avoid acids
- heat in the display case, sunlight and artificial light: use caution
treated (Only after these treatments: dyeing)
Durability and wearing
Treatments and identification leads
Registered treatmentsThe treatments registered for Shell are dyeing and coating. Values not givenDyeing has the status treated, an unstable effect and common market prevalence; coating has the status treated, with stability and prevalence both entered as “—”, meaning the cited source gives no value, not “none”. Identification cluesIdentification leads are registered for both dyeing and coating, citing GB/T 16553—2017; the standard cited for the identification leads can be followed only as a reference and does not directly govern Shell.
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| Treatment | Market frequency (CIBJO) | Stability (CIBJO) | GB/T 16552 category | JJA/AGL listing | Identification leads |
|---|---|---|---|---|---|
| dyeingStatus: treated | commonly | unstable | Treatment | — | See identification leads |
| coatingStatus: treated | — | — | Graded — see §5.4.1, Table 1 | — | See identification leads |
| colouring (JJA category 7, includes dyeing) | — | — | — | colouring (JJA category 7, includes dyeing) | — |
Where each treatment acts (schematics): Dyed · Coated
“—” means the cited source gives no value for that item, not “none”. Source: CIBJO Gemstone Book 2022 · GB/T 16553—2017; GB/T 16552—2017 Table B.1; 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
Besides Shell, the name register records "Conch Shell" and "Pink Conch", for which no restriction on use as a name is recorded (JJA/AGL Gemstone Nomenclature 2025 p.13); 2 further names in non-Latin scripts are listed in the name register below (2 with no restriction recorded on use as a name).
Standard and listing namesThe GB/T 16552—2017 standard name for Shell is shell (Table A.3), and the suggested listing name is Shell (stating species, part and treatment); it is also called Conch Shell or Pink Conch. Names in four languagesNames are registered in four languages: Simplified Chinese, Traditional Chinese, English (Shell) and Japanese (the GSJ (Japan) formal name). Trade and mineralogical namesThe mineralogical name requires the genus and species and the shell layer to be stated. Institution usageOn authority wording, CIBJO records Shell (CIBJO Gemmological Laboratories Book 2024); GIA, FTC and Gem-A are unchecked, and bodies without a recorded wording show the English name Shell, which does not represent their position. Candidate search termsThe JJA/AGL (Japan) 2025 handbook, p. 13, also registers Conch Shell and Pink Conch together with their Japanese transliterations, which are used only as candidate search terms. National standard namesGermany (RAL) uses Muschel / Perlmutt, and the EU uses Shell / Mother-of-Pearl.
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.
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| Name | Type | Matching | Use as a name | Basis |
|---|---|---|---|---|
| no restriction recorded (4) | ||||
| Conch ShellEnglish | narrower name (variety or subtype) | matched automatically | no restriction recorded | JJA/AGL Gemstone Nomenclature 2025 p.13 |
| Pink ConchEnglish | transliteration | matched automatically | no restriction recorded | JJA/AGL Gemstone Nomenclature 2025 p.13 |
| コンク・シェルJapanese | transliteration | search candidate only | no restriction recorded | JJA/AGL Gemstone Nomenclature 2025 p.13 |
| ピンク・コンクJapanese | transliteration | search candidate only | no restriction recorded | JJA/AGL Gemstone Nomenclature 2025 p.13 |
How each authority words this name: see Names › Authority wording.
- GSJ (Japan) formal name
- 貝殻／シェル
- Chinese formal name
- 贝壳 (GB/T 16552—2017 Table A.3)
- Mineralogical name
- Molluscan shell material; species and layer must be specified
- Trade names and synonyms
- Conch Shell (narrower name (variety or subtype)) · Pink Conch (transliteration)
Four-language names
- 简体中文
- 贝壳
- 繁體中文
- 貝殼
- English
- Shell
- 日本語
- 貝殻／シェル
National and regional formal names
- Germany (RAL)
- Muschel / Perlmutt
- European Union
- Shell / Mother-of-Pearl
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
GB/T Table B.1The methods listed for Shell in the Shell row of GB/T 16552—2017, Annex B, Table B.1 are coating and dyeing. Coating improves or changes lustre, colour and other aspects of appearance, and its category is graded; dyeing improves or changes colour, and its category is treatment. What Table B.1 is and how the grades are defined are on the Gem treatments page. JJA/AGL designationsIn the Japanese JJA/AGL 2025 listing, Shell is listed under the species Conch Shell, in pink, brown and white, with a tier marked untreated and the note natural pink conch shell; the JJA/AGL listing also gives the species as shell, with the colouring entry noted as including dyeing and classed as dyeing. How to read the JJA/AGL table is explained on the Gem treatments page.
GB/T 16552-2017, Annex B, Table B.1
Table B.1, row “Shell” (p.18):
This table scrolls sideways on narrow screens.
| Method | Effect | Category |
|---|---|---|
| Coating | Improves or changes lustre, colour and other aspects of appearance | Graded — see §5.4.1, Table 1 |
| Dyeing | Improves or changes colour | Treatment |
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
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| Gem name | Species | Colour | Listed in the table | Notes |
|---|---|---|---|---|
| Shell | Conch Shell | pink, brown, white | an untreated tier is listed | (effect/alias column) natural pink conch; no dedicated entry on this site; shown on the broader entry |
| Shell | Shell | an untreated tier is listed; colouring (JJA category 7, includes dyeing) (Dyed) |
JJA/AGL definitions and nomenclature (2025 revision), table of principal gem names, p.13
How to read the JJA/AGL table: see the Gem treatments page.
What it is and how it's identified
The registered material facts for Shell: the overall structure has an inorganic part of radiating aggregates, with aragonite orthorhombic and calcite trigonal, and an amorphous organic part; Mohs hardness is 3–4, cleavage is generally not seen on an aggregate, and untreated shell effervesces with a drop of hydrochloric acid; for treated shell, the stability of dyeing is unstable. Density is 2.7–2.89 g/cm³; this site notes that the cited clause gives 2.86 with a stated tolerance (+0.03, −0.16), from which the limits are derived. Refractive index is 1.53–1.68; this site notes that the cited clause gives the readings commonly obtained by the spot method, which are typical values rather than absolute limits. The optic character is aggregate and birefringence cannot be measured on an aggregate; for untreated Shell, the quality factor (lustre) is greasy to pearly lustre, and the optical effect (iridescence) is visible.
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”.
Structure
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
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
Durability
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
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
Shell — cleavage: generally not seen on an aggregate
GB/T 16553—2017
- Does this standard apply
- applies to this entry
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
Shell — stability: effervesces on contact with hydrochloric acid
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
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
For Shell, the stability of dyeing is “unstable”.
CIBJO Gemstone Book 2022
- Treatment state
- treated
- Treatment
- dyeing
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Physical properties
Shell — density: 2.7–2.89 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- 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
Shell — optic character: aggregate
GB/T 16553—2017
- Does this standard apply
- applies to this entry
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
Shell — refractive index: 1.53–1.68
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- 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
Shell — birefringence: not measurable on an aggregate
GB/T 16553—2017
- Does this standard apply
- applies to this entry
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
Shell — pleochroism: not measurable on an aggregate
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
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
Shell — fluorescence (overall): varies with colour or shell species
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
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
Shell — spectrum (UV-visible): non-characteristic
GB/T 16553—2017
- Does this standard apply
- applies to this entry
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
Shell — spectrum (infrared): Carbonate-ion vibration in aragonite produces the diagnostic mid-IR bands
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-22
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (locator checked 2026-09-22)
- Fact checked on
- 2026-09-22
Shell — optical effect (iridescence): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
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
Shell — magnification: layered texture, layers stacked on the surface, a flame-like pattern in places.
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
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
Shell — body colour: white, grey, black, brown, yellow, pink, etc.
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- Qualification
In chapter 5 of GB/T 16553—2017, the colour entries of Qingtian Stone, Rhodochrosite, Chicken-blood Stone and other variety clauses also name white or a whitish colour.
- General note
- colour alone is not identity
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
Shell — quality factor (lustre): greasy to pearly
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
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
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
Testing and market
The coating leads for Shell apply to coated shell: abnormal surface lustre under magnification, the coating peeling off in places, abnormal refractive index, and characteristic peaks of the coating in infrared and Raman spectra; these are cited from GB/T 16553—2017, which serves only as a reference for Shell and does not govern it directly. The dyeing leads apply to dyed shell: uneven colour under magnification, with the dye mostly gathered in fractures, grain boundaries or growth defects; possible distinctive fluorescence of the dye under long-wave and short-wave UV; colour coming off when wiped with solvents such as acetone or anhydrous ethanol; and some naturally coloured and dyed shells behaving differently in Raman testing; these are also cited from GB/T 16553—2017, which serves only as a reference for Shell. There is no synthetic Shell on the market. Among Shell on the market, dyeing is common. The laboratory protocol of the CIBJO Gemmological Laboratories Book 2024 calls for particular checks on Shell for dyeing and lustre enhancement; the required tests and what each method covers are given in the protocol table on the laboratory testing page.
The tests the CIBJO laboratory protocol requires for this material, and what each method means, are in the protocol table on the laboratory testing page: §6.2.26.
How far testing can go
Shell that has undergone coating can be identified by the following features: Under magnification the surface luster is abnormal and the film can be seen peeling off; the refractive index is abnormal; infrared and Raman spectra show characteristic peaks of the film layer.
GB/T 16553—2017
- Treatment state
- treated
- Does this standard apply
- can be followed as a reference only
- Treatment
- coating
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (coating) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Shell that has undergone dyeing can be identified by the following features: Under magnification the colour is unevenly distributed and mostly concentrated in fissures, between grains or at growth defects; an unusual fluorescence from the dye may appear under long- and short-wave UV; wiping with acetone or absolute ethanol can lift the colour; Raman spectra separate some naturally coloured shell from dyed shell.
GB/T 16553—2017
- Treatment state
- colour treated
- Does this standard apply
- can be followed as a reference only
- Treatment
- dyeing
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.10 (dyeing) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Shell — 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 2026-09-22
- Source
- Fact checked on
- 2026-09-22
For Shell in trade, the reported frequency of dyeing is “commonly”.
CIBJO Gemstone Book 2022
- Treatment state
- treated
- Treatment
- dyeing
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Shell — what the CIBJO laboratory protocol says to watch for: dye, lustre enhancement
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- any treatment state
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.
Clause-level definitions
Shell has a direct definition in the CIBJO Gemmological Laboratories Book 2024 under the term Shell; the cross-check result is defined directly by CIBJO, also appearing in the GB/T annex. The definition visible in the CIBJO Gemmological Laboratories Book 2024 is that shell is the calcareous outer part of a mollusc's body.
This table scrolls sideways on narrow screens.
| Term | Clause | Definition | Cross-check |
|---|---|---|---|
| Shell | 7.2.2.10 | Shell is the calcareous outer part of a mollusc’s body. It mainly consists of calcium carbonate and an organic matrix (conchiolin) Distinction criteria | Defined directly by CIBJO; also present in the GB/T annex. |
Evidence and sources
Authority basis and clause sources
Sources
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 (Shell) is marked.
- Shell
Sub-entries (2)
This table scrolls sideways on narrow screens.
| Page | Content | Status |
|---|---|---|
| Browsing family | Pearl and molluscan shell materials | Live |
| Treatments recorded for this material | Coated, Dyed | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the 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; 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.