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
Mother-of-Pearl / Nacre
Also known asMOP
The nacreous (pearly) layer from the inside of shells; it is not pearl itself and does not refer to any one particular shellfish. 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.
Questions people ask about Mother-of-Pearl / Nacre
Every sentence below is followed by the registered fact it rests on; answers add no new facts and promise no outcome.
Q1How do you know mother-of-pearl is genuine and not plastic?
Looks alone struggle to tell: according to the parent entry Shell, shell resembles imitation or treated shell material in appearance, and identification requires instrumental testing of structure and composition in a laboratory.CIBJO Gemstone Book 2022 (via parent entry Shell)Genuine mother-of-pearl is the inner layer of a mollusc shell, made of aragonite in a brick-type arrangement combined with an organic matrix of proteins and polysaccharides.G&G Fall 2021Its lustre is greasy to pearly.GB/T 16553—2017Plastic imitations have a long history: the Smithsonian's National Museum of American History notes that celluloid could be made to imitate mother-of-pearl.Smithsonian NMAHWhether one particular bead is natural, treated or synthetic — only a laboratory report can settle that.What this page can answer
Q2What is mother-of-pearl, and is it the same as pearl?
CIBJO defines mother-of-pearl as the iridescent, smooth, hard coating on the inner surface of the shell in certain mollusc species; its scientific name is nacre.CIBJO Pearl Book 2024It is not a pearl: pearl and shell nacre are the same material, but mother-of-pearl itself is the inner-shell layer, not a pearl.G&G Fall 2021Both shell and pearl nacre are secreted by cells of the mantle, which produce aragonite and organic matrix.G&G Fall 2021Under CIBJO's Pearl Book the term mother-of-pearl may not be used to describe imitation pearls.CIBJO Pearl Book 2024
Q3Why does mother-of-pearl shimmer, and why does its colour vary by shell?
The ordered arrangement of nacre, aragonite crystallites plus organic matrix, gives mother-of-pearl its pearly lustre.GIA Pearl Description · G&G Fall 2021It comes from marine or freshwater molluscs, and the nacre colour differs by species, as in gold-lipped and black-lipped shells.G&G Fall 2021The gold-lipped oyster takes its name from the golden outer edge of its mother-of-pearl layer.GIA Pearl Description
Q4Does mother-of-pearl have calming or healing powers?
There is no scientific evidence that mother-of-pearl has healing powers: the UK advertising regulators ASA and CAP state that they have not seen evidence that crystal therapy can treat medical conditions.ASA/CAP guidance (UK)
Q5How should mother-of-pearl be cleaned and looked after?
Keep it out of ultrasonic cleaners: CIBJO lists it among the stones that ultrasonic cleaning can damage.CIBJO Gemstone Book 2022It is porous, so keep it away from coloured liquids, and it is particularly vulnerable to acids, so keep it away from acids.CIBJO Gemstone Book 2022
Q6Does mother-of-pearl scratch easily?
Yes: CIBJO notes that its low hardness makes it prone to scratching, so it should be worn with care.CIBJO Gemstone Book 2022China's national standard gives shell, as a class, a Mohs hardness of 3–4; that is a class figure, not a measurement of mother-of-pearl itself.GB/T 16553—2017
Q7Is mother-of-pearl often dyed?
Often: CIBJO's Gemstone Book lists mother-of-pearl as commonly dyed and only occasionally untreated.CIBJO Gemstone Book 2022Dyeing and similar treatments are not permanent, so dyed pieces should be kept away from all solvents, including dish-washing liquid, and from chemicals and heat.CIBJO Gemstone Book 2022Dyed mother-of-pearl may fade or revert to its original colour in strong light, so it should not be worn or left in strong light for long periods.CIBJO Gemstone Book 2022
Sources cited in these answers ASA/CAP guidance (UK)
What this page can answer
This page covers
- How Mother-of-Pearl / Nacre forms and what gives its colourFormation setting, process and timescale; where its colour and optical effects come from, each finding graded and sourced
- How to identify Mother-of-Pearl / NacreHow far lab testing can go
- Treatments and enhancements of Mother-of-Pearl / NacreThe enhancements and treatments the GB/T and JJA/AGL tables list
- Caring for and wearing Mother-of-Pearl / NacreCleaning, heat, chemicals and light, as the cited sources give them
- Hardness, density and refractive index of Mother-of-Pearl / NacreEach value with its source and check date
- Mother-of-Pearl / Nacre 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 Mother-of-Pearl / NacreThe 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
Mother-of-pearl (nacre) is the inner layer of a mollusc shell, not a pearl. It is secreted by the outer ectoderm epithelium cells of the mantle: the cells produce calcium carbonate (mainly aragonite) in a brick-type arrangement together with an organic matrix of proteins and polysaccharides; together these are called nacre or mother-of-pearl (MOP). The color of the shell's mother-of-pearl layer (e.g. the gold lip of a gold-lipped oyster, the dark colors of a black-lipped oyster) is often related to the nacre color of the cultured pearls it produces. Pearl and shell nacre are the same material, but mother-of-pearl is the inner-shell layer.
Scope: Covers the biogenic origin and material composition of mother-of-pearl (the nacreous layer of shells), and its relationship to and differences from pearls; does not apply to pearls themselves or to imitation pearls.
Sources G&G Fall 2021 · CIBJO Pearl Book 2024
Where it forms
Mantle and inner shell surface of a mollusk: epithelium cells secrete nacre forming the shell's inner layer.
Sources G&G Fall 2021
Marine or freshwater mollusks; shell nacre color differs by species (gold-lipped, black-lipped, etc.).
Sources G&G Fall 2021
How it forms, step by step
The outer ectoderm epithelium cells of the mantle secrete calcium carbonate (mainly aragonite) and organic matrix.
Aragonite is arranged in a brick-type pattern with the organic matrix and is deposited as nacre.
Nacre is built up layer by layer to form the shell's inner layer, i.e. mother-of-pearl.
Link to appearance
The ordered arrangement of nacre (aragonite crystallites plus organic matrix) gives mother-of-pearl its pearly luster; the shell's nacre color is often related to the nacre color of the cultured pearls it produces.
Sources GIA Pearl Description · G&G Fall 2021
Timescale
Sources give no growth duration or absolute age for shell nacre; deposition rate depends on species and environment.
Sources G&G Fall 2021
Related base materials
- Mollusc shell: inner-layer-of | Mother-of-pearl (nacre) is the inner layer of the shell, secreted by the epithelial cells of the mantle; it is not pearl
Supporting findings
Shell and pearl nacre is secreted by mantle epithelium cells, which are responsible for shell and pearl formation by producing aragonite and organic matrix.
Evidence grade AScope: Describes the nacre secretion mechanism, from Pinctada maxima research.
Recorded localities
This is an organic material; its localities are the harvest or culture areas (waters or species ranges) recorded by authoritative sources.
North America
- United StatesFreshwater mussel shell for mother-of-pearl buttons, late 1800s to 1960s
Sources CIBJO Pearl Book 2024
- CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1)
Seas and coasts
- Red SeaBlack-lipped pearl oyster; historic centre for mother-of-pearl
Sources CIBJO Pearl Book 2024
- CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1)
- Sudan waters, Red SeaBlack-lipped pearl oyster, for mother-of-pearl
Sources CIBJO Pearl Book 2024
- CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1)
- North-western and western Australian watersSilver-lipped Pinctada maxima
Sources CIBJO Pearl Book 2024
- CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1)
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
The hue of a shell's mother-of-pearl layer generally matches the nacre colour of the cultured pearls grown in it; the gold-lipped oyster takes its name from the golden outer edge of that mother-of-pearl layer.
Evidence grade BScope: Describes the relation between shell nacre color and cultured pearl nacre color, not a quantitative chemistry.
Sources GIA Pearl Description
Other research findings
Mother-of-pearl (nacre) is the inner layer of a mollusc shell, made of aragonite in a brick-type arrangement combined with organic matrix (proteins and polysaccharides).
Evidence grade AScope: Authoritative description of nacre composition, applicable to both shell inner layer and pearl nacre.
Mother-of-pearl is the inner-shell layer, not a pearl: although pearl and shell nacre are the same material (nacre), mother-of-pearl itself is not a pearl.
Evidence grade AScope: Naming/identity boundary; the source calls the nacre of both shell and pearl nacre/MOP.
CIBJO defines mother-of-pearl as the iridescent, smooth, hard coating found on the inner surface of the shell in certain mollusk species; the scientific term for it is nacre (5.126).
Evidence grade AScope: The naming/identity definition (Pearl Book clause 5.123); mother-of-pearl is the nacre layer on the inner shell surface.
Sources CIBJO Pearl Book 2024
Plastic look-alikes of mother-of-pearl have a long history: the Smithsonian's National Museum of American History notes that celluloid, regarded as the first semi-synthetic plastic, could be made to imitate costly materials including mother-of-pearl, ivory and tortoiseshell, and was used for affordable fancy goods from the late nineteenth century.
Evidence grade BScope: A historical statement about celluloid only. It does not cover modern resins, does not say how common such imitations are today, and gives no method for telling plastic from shell.
Under the CIBJO Pearl Book, "mother of pearl" may not be used as a description for imitation or simulated pearls; imitations must be called imitation or simulated.
Evidence grade AScope: A trade nomenclature rule for describing imitation pearls; it does not regulate the use of the word for genuine shell nacre.
Sources CIBJO Pearl Book 2024
CIBJO's Gemstone Book lists mother-of-pearl as commonly dyed and only occasionally untreated. It rates the dyed material as unstable and adds the care note for dyed and impregnated stones: the treatment is not permanent, so keep it away from solvents (including dish-washing liquids), chemicals and heat.
Evidence grade AScope: Frequency words are CIBJO's trade-level estimates, not measured market shares; they say nothing about any particular piece.
Sources CIBJO Gemstone Book 2022
Limits of this research
- Research status: Formation, occurrence or other material-specific findings found in authoritative sources
- Sources give no growth duration or absolute age for shell nacre.
- This record only covers mother-of-pearl versus pearl distinction, not the origin of other shell layers or the whole shell.
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
- Mother-of-Pearl / nacre
GB/T 16552—2017 5.1.1 b)
Construction or treatment status
Natural identity; treatment status unknown
Treatments recorded for this material: Coated (via parent material), 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
Mother-of-Pearl / Nacre is Nacre (mother-of-pearl) from mollusc shell; use "Mother-of-Pearl / nacre" for listings, and disclose any known treatments.
What this means for you
Before buying, check the recommended listing name "Mother-of-Pearl / nacre" 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.
Care
Mother-of-Pearl / Nacre — 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 2026-09-26
- Source
- CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §8 Annex C, Mother of Pearl, p.76; §6.2 j (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Mother-of-Pearl / Nacre — 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
- treated
- Only after these treatments
- dyeing
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §8 Annex C, Mother of Pearl, p.76; §6.2 f (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Mother-of-Pearl / Nacre — 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 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Mother-of-Pearl / Nacre — 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 2026-09-26
- Source
- CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §8 Annex C, Mother of Pearl, p.76; §6.2 k (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Mother-of-Pearl / Nacre — 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 2026-09-26
- Source
- CIBJO Blue Book — Official Gemstone Book (Coloured Stone Commission 2022) (CIBJO): §8 Annex C, Mother of Pearl, p.76; §6.2 a (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
The care findings for Mother-of-Pearl / Nacre all come from the CIBJO Blue Book (Official Gemstone Book, Coloured Stone Commission 2022): Mother-of-Pearl / Nacre must not be cleaned ultrasonically, in any treatment state; for treated material, and specifically dyed material, it can fade or revert to the original colour in strong light, so it should not be worn or left in strong light for long periods; in any treatment state it is porous, so it should not touch coloured liquids, and it is particularly vulnerable to acids and should be kept away from them; for treated material, and specifically dyed material, dyeing, oiling, resin impregnation, waxing and plastic impregnation are all non-permanent, so it should be kept away from all solvents (including all kinds of detergent), chemicals and high temperatures; and in any treatment state it is soft and scratches easily, so it should be worn with care.
This table scrolls sideways on narrow screens.
| Question | Matching entries |
|---|---|
| Can it go in an ultrasonic or steam cleaner? | care (cleaning) |
| 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 |
| Contact with acids, alkalis and household 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; Treatments with dye, oil, resin, wax or plastic are not permanent; keep it away from all solvents (including dish-washing liquids), chemicals and heat |
| Wearing limits (knocks, settings) | care (wear) |
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
- 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
treated (Only after these treatments: dyeing)
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 | — | — |
| colouring (JJA category 7, includes dyeing) | — | — | — | colouring (JJA category 7, includes dyeing) | — |
“—” means the cited source gives no value for that item, not “none”. Source: GB/T 16552—2017 Table B.1 (row for Shell); 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 Mother-of-Pearl / Nacre, the name register records "MOP", for which no restriction on use as a name is recorded; one further name in a non-Latin script is listed in the name register below (1 with no restriction recorded on use as a name).
Recommended listing nameThe suggested listing name for Mother-of-Pearl / Nacre is mother-of-pearl; the corresponding name in GB/T 16552—2017 Table A.3 is shell, and mother-of-pearl itself is not listed in the original GB/T 16552—2017. Trade and mineralogical namesThe mineralogical name is nacre from mollusc shell, in English Nacre; the trade name/synonym is MOP. Names in four languagesFour-language names are given in Simplified Chinese, Traditional Chinese, English (Mother-of-Pearl / Nacre) and Japanese. In the name register, MOP is the English abbreviation, and a Simplified Chinese synonym meaning nacre layer is kept only as a candidate search term, based on the same term in GB/T 18781—2023. Institution usageThe wording of GIA, FTC, CIBJO and Gem-A for this name is not yet verified by this site; the name shown is the entry's own English name, Mother-of-Pearl / Nacre, which does not represent the position of GIA, FTC, CIBJO or Gem-A. Japanese namesThe formal name shown for Japan's GSJ is the entry's own Japanese name, and the wording of Japan's GSJ for this name is likewise not yet verified by this site.
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 (2) | ||||
| MOPEnglish | short form | matched automatically | no restriction recorded | editorial ruling (no clause cited) |
| 珍珠层Simplified Chinese | synonym | search candidate only | no restriction recorded | GB/T 18781—2023 3.5 |
How each authority words this name: see Names › Authority wording.
- GSJ (Japan) formal name
- マザーオブパール／真珠母（真珠層） (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)
- 贝壳 (GB/T 16552—2017 Table A.3)
- Mineralogical name
- Nacre (mother-of-pearl) from mollusc shell
- Trade names and synonyms
- MOP (short form)
Four-language names
- 简体中文
- 贝母
- 繁體中文
- 貝母
- English
- Mother-of-Pearl / Nacre
- 日本語
- マザーオブパール／真珠母（真珠層）
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 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.
JJA/AGL (Japan) table of principal gem names, 2025
This table scrolls sideways on narrow screens.
| Gem name | Species | Colour | Listed in the table | Notes |
|---|---|---|---|---|
| Mother of Pearl | 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 definition of Mother-of-Pearl / Nacre is a CIBJO trade definition from an organisational handbook, not a national standard: the smooth, hard, iridescent lining on the inner surface of the shells of certain molluscs, scientifically called nacre. The structure registered for shell (the whole class) is: the inorganic part is a radially arranged aggregate, with aragonite orthorhombic and calcite trigonal, and the organic part has no crystalline structure. Also taking values for shell (the whole class), Mohs hardness is 3–4, a range for the whole class rather than a measurement of Mother-of-Pearl itself; density is 2.7–2.89 g/cm³, with the limits derived from the cited clause value of 2.86 and its stated tolerances of +0.03 and −0.16; refractive index is 1.53–1.68, which this site notes is a reading the cited clause gives as often obtained by the spot method, a common value rather than an absolute limit. For shell (the whole class), optic character is aggregate and the optical effect (iridescence) visible; untreated, the quality factor (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 Mother-of-Pearl / Nacre 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 Mother-of-Pearl / Nacre (how to read class-level values).
Definition
Mother-of-Pearl / Nacre: the smooth, hard, iridescent coating on the inner shell surface of some species, e.g., Pinctada maxima (9.60), Haliotis sp., (9.1) Turbo sp., and varieties of Unio sp. of mollusc that is scientifically known as nacre (5.126). Usually, but not always, natural pearls produced by a particular mollusc have the same colour, composition and general quality as the mother-of-pearl of that mollusc.
CIBJO Pearl Book 2024
- Qualification
CIBJO trade definition from an institutional manual, not a national standard. The English text quotes the full definition at §5.123 of the Pearl Book 2024.
Source & check 2026-09-25
- Source
- CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.123, p.34 (locator checked 2026-09-25)
- Fact checked on
- 2026-09-25
Structure
Mother-of-Pearl / Nacre — 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
Mother-of-Pearl / Nacre — 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
Mother-of-Pearl / Nacre — 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
Mother-of-Pearl / Nacre — 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
Mother-of-Pearl / Nacre — 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
Mother-of-Pearl / Nacre — 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
Mother-of-Pearl / Nacre — 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
Mother-of-Pearl / Nacre — 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
Mother-of-Pearl / Nacre — 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
Mother-of-Pearl / Nacre — 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
Related CIBJO terms
- Conchiolin
A mixture of beta-chitin and glycoproteins constituting the organic portion of nacre (C32H48N2O11).
CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.49, p.27
- Nacre
biogenic material of nacreous natural (5.132) and cultured pearls as well as the lining of the inner part of the producing mollusc shell. Nacre is composed of layers of microscopic platelets of biomineralised aragonite (calcium carbonate), bound together by a fine network of a complex scleroprotein called conchiolin (5.49). This characteristic structure produces optical effects (orient, overtone) from within the pearl. Nacre is secreted from the mantle (5.114) of certain bivalves (5.154) and some gastropods.
CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.126, p.35
- Nacreous
composed of nacre (5.126).
CIBJO Blue Book — Pearl Book (Pearl Commission 2024-1) (CIBJO): §5.129, p.35
Definitions are quoted verbatim from the cited CIBJO Blue Book; […] marks an excerpt, and the full definition is at the cited clause.
Pearl-producing molluscs (CIBJO Annex D): §9.1 Abalone · §9.10 Australian south-sea pearl oyster · §9.60 Pinctada maxima
Testing and market
The CIBJO laboratory protocol covers Mother-of-Pearl / Nacre under “Shell” (§6.2.26): see identification on the Shell entry; the required tests are listed on the CIBJO laboratory protocol table for Shell.
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
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 (Mother-of-Pearl / Nacre) 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 | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Mother-of-Pearl / Nacre 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.