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
Coral
Also known ascommon coral · Precious coral (conditional name)
A biogenic skeletal material whose composition varies by taxon (calcareous or organic); its CITES status also differs by species. 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 Coral
Every sentence below is followed by the registered fact it rests on; answers add no new facts and promise no outcome.
Q1How can you tell real coral from glass, plastic or dyed imitations?
Precious and common corals cannot be told apart from imitations, dyed material or filled material by colour and appearance alone.CIBJO Coral Blue Book 2024Their identity is bound up with composition and structure: precious coral is biomineralised calcium carbonate, while some pink-to-red look-alikes are dyed and impregnated aragonite of a different composition.CIBJO Coral Blue Book 2024No synthetic coral is commercially available.CIBJO Gemstone Book 2022Whether one particular bead is natural, treated or synthetic — only a laboratory report can settle that.What this page can answer
Q2Is coral dyed or otherwise treated, and how is it detected?
Coral can be dyed: under magnification dyed coral's colour is uneven and concentrated in fissures, between grains or in surface hollows, and wiping with acetone or absolute ethanol can lift the colour.GB/T 16553—2017Raman and UV-visible spectra separate pink-red calcareous coral from dyed coral.GB/T 16553—2017In filled coral, the filled parts show a different surface lustre and may hold gas bubbles under magnification, and under long-wave UV they mostly fluoresce differently from the rest of the coral.GB/T 16553—2017Coated coral shows an abnormal surface lustre under magnification, with the film peeling off in places.GB/T 16553—2017Bleaching, which removes surface impurities to improve colour and appearance, is hard to detect.GB/T 16553—2017AGTA marks orange and red coral assembled with polymers and dyed as needing special care, away from chemicals and solvents.AGTA Gemstone Information Manual, 17th ed.
Q3How should coral be cleaned?
CIBJO advises soft leather and gentle brushing, and no ultrasonic cleaner, because coral is porous and especially vulnerable to ultrasonic cleaning.CIBJO Coral Blue Book 2024GIA's durability tables likewise say to avoid ultrasonic and steam cleaning.Gems & Gemology 1987 (Martin)CIBJO also notes that some corals are porous, so they should be kept from coloured fluids, and that acids and solvents such as nail-varnish remover dissolve them.CIBJO Coral Blue Book 2024When not being worn, keep pieces apart so they do not scratch one another.CIBJO Coral Blue Book 2024
Q4Can you wear coral jewellery every day?
With care: CIBJO notes that some corals scratch easily because of their low hardness, so they should be worn carefully.CIBJO Coral Blue Book 2024China's national standard gives calcareous coral, as a class, a Mohs hardness of 3–4.5.GB/T 16553—2017For horny coral, as a class, it gives 2–3.GB/T 16553—2017Some corals can crack if they lose structural water, so keep them from heat, drying environments and sudden temperature changes.CIBJO Coral Blue Book 2024For settings, prong, bezel and channel call for caution, while flush and pavé are best avoided.Gems & Gemology 1987 (Martin)
Q5What is precious coral, and where does it grow?
Coral is the skeletal material of marine invertebrates of the class Anthozoa (phylum Cnidaria), formed by nature without human intervention.CIBJO Coral Information SheetPrecious corals belong only to three genera of the family Corallidae, Corallium, Pleurocorallium and Hemicorallium, and take a porcelain-like lustre once polished.CIBJO Coral Information SheetPrecious corals consist chiefly of calcium carbonate laid down by biological mineralization.CIBJO Coral Information SheetHorny coral, by contrast, is described in China's national standard as made up almost entirely of organic matter.GB/T 16553—2017Precious corals are typically deep-sea species living from 50 to 2000 metres below the surface, while reef corals inhabit shallow water.CIBJO Coral Information Sheet
Q6Does coral fade in sunlight?
Some corals can: CIBJO notes that strong light can fade them or turn them back to their original colour, so they should not be worn or left in such light for long.CIBJO Coral Blue Book 2024Some colour-treated corals can also fade or revert to their original colour, and should not be kept for long in strong natural, artificial or display lighting.CIBJO Coral Blue Book 2024For display, artificial light is rated relatively safe, while display-case heat and sunlight call for caution.Gems & Gemology 1987 (Martin)
Q7What makes good-quality coral?
CIBJO's reference guide for retailers, describing precious coral, says quality factors differ by species, but size and uniform colour usually matter, especially in strands, where matching is of primary importance.CIBJO Retailers' Reference Guide (2021)Large, fine art carvings in rich pink to deep red are highly prized and very rare.CIBJO Retailers' Reference Guide (2021)
Q8What does coral symbolize, and does it have healing powers?
There is no scientific evidence that coral 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)Its recorded cultural role is as a birthstone: Japan's JJA 2021 revised list puts coral under March.Cultural recordsMuseum collections include a Peruvian coral necklace dated before 1532, showing coral used as an ornamental material in pre-Columbian America.Cleveland Museum of Art 1940.499 · The Met 43.164 +3
Sources cited in these answers ASA/CAP guidance (UK)
What this page can answer
This page covers
- How Coral forms and what gives its colourFormation setting, process and timescale, each finding graded and sourced
- How to identify CoralIdentification points from the research literature; how far lab testing can go and whether a synthetic exists
- Treatments and enhancements of Coral4 registered treatments: status, stability, how common they are and identification leads
- Caring for and wearing CoralCleaning, heat, chemicals and light, as the cited sources give them
- Hardness, density and refractive index of CoralEach value with its source and check date
- Coral 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 CoralHow people have used it, with museum objects
- Listing and disclosing CoralThe listing name to use; what must be disclosed before sale
- Standard clauses that define CoralWhich 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
Coral is the collective name for the skeletal material of colonial marine invertebrates in the class Anthozoa, phylum Cnidaria, formed by nature without human intervention. Precious corals used in jewellery and decoration are chiefly the red, pink and white varieties, which take a porcelain-like lustre once polished, and belong only to three genera of the family Corallidae: Corallium, Pleurocorallium and Hemicorallium. Their gemmological properties stem essentially from this calcium carbonate (calcitic) makeup, mostly calcium carbonate laid down by biological mineralization in aragonitic and/or calcitic structures. Precious corals are typically deep-sea species dwelling from 50 to 2000 metres, while reef corals inhabit shallow water. This source focuses on material classification and trade and does not describe the physiologic mechanism by which polyps secrete and build the skeleton.
Scope: Covers the basic properties, classification and habitat depths of precious coral as a biogenic gem material; evidence in this source is insufficient on the specific physiological and growth mechanisms of skeletal deposition by coral polyps.
Sources CIBJO Coral Information Sheet
Where it forms
Deep-sea settings: precious corals are typically species of the deep ocean, dwelling from roughly 50 to 2000 metres below the sea surface.
Sources CIBJO Coral Information Sheet
Shallow-water reefs: reef corals live in shallow water but are varieties not used in jewellery.
Sources CIBJO Coral Information Sheet
How it forms, step by step
Colonies of coral polyps grow on the seabed (precious corals usually in deep water from 50 to 2000 metres).
Sources CIBJO Coral Information Sheet
The colony's skeleton is built largely of calcium carbonate laid down by biological mineralization in aragonitic and/or calcitic structures.
Sources CIBJO Coral Information Sheet
After the coral dies the branches settle and accumulate, and can form geological deposits (such as Sciacca coral) that are considered sedimentary formations.
Sources CIBJO Coral Information Sheet
Link to appearance
Precious corals show a porcelain-like lustre after polishing, in chiefly red, pink and white colors, their gemmological properties being essentially a result of their calcium carbonate (calcitic) composition. In deep-sea varieties the white-to-pink background is decorated with reddish veins and spots caused by changes in water pressure and temperature.
Sources CIBJO Coral Information Sheet
Timescale
The timescale here is biological growth and lifespan: red coral colonies in populations that are not harvested may grow to roughly 50 centimetres tall, and their maximum lifespan has recently been estimated at about 106 years; no numeric geological age is provided for specific coral deposits.
Sources CIBJO Coral Information Sheet
Related base materials
- Coral polyps (phylum Cnidaria): Coral is a skeletal material formed by colonies of coral polyps and is a biogenic material
Supporting findings
Coral is the skeletal material of marine invertebrates of the class Anthozoa (phylum Cnidaria), formed by nature without human intervention.
Evidence grade AScope: This statement comes from the CIBJO coral information sheet and defines material classification rather than growth physiology.
Sources CIBJO Coral Information Sheet
Precious corals are typically species of the deep sea, dwelling from 50 to 2000 metres below the surface, while reef corals inhabit shallow water.
Evidence grade AScope: This is a generalization of habitat depth; individual species' depth ranges may fall outside it.
Sources CIBJO Coral Information Sheet
Non-harvested red coral colonies can reach about 50 centimetres in height, with maximum life spans recently estimated at about 106 years.
Evidence grade AScope: This lifespan applies to non-harvested Corallium rubrum populations and does not represent all coral species.
Sources CIBJO Coral Information Sheet
Recorded localities
This is an organic material; its localities are the harvest or culture areas (waters or species ranges) recorded by authoritative sources.
Europe
- Waters off Sciacca, Sicily, ItalyBroken Corallium rubrum branches from modern sedimentary deposits
Sources CIBJO Coral Blue Book 2024
Seas and coasts
- Mediterranean SeaA major long-standing source of pink-to-red ornamental coral (Corallium rubrum)
Sources Gems & Gemology Spring 2007 · CIBJO Coral Blue Book 2024
- Atlantic coast of North Africa, Spain and PortugalRange of Corallium rubrum; printed as 'western Atlantic coast'
Sources CIBJO Coral Blue Book 2024
- Waters off Japan
Sources Gems & Gemology Spring 2007 · CIBJO Coral Blue Book 2024
- Waters off China
Sources Gems & Gemology Spring 2007
- Waters off Taiwan, China
Sources CIBJO Coral Blue Book 2024
- South China Sea near Vietnam
Sources CIBJO Coral Blue Book 2024
- Waters off northern Philippines
Sources CIBJO Coral Blue Book 2024
- Waters off Hawaii, United States
Sources Gems & Gemology Spring 2007 · CIBJO Coral Blue Book 2024
- Midway and the Emperor Seamounts to the northwest, North Pacific
Sources CIBJO Coral Blue Book 2024
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.
Human use and museum objects
An early coral ornament is Cleveland 1940.499, a necklace (before 1532, Peru, coral), showing coral used as an ornamental material in pre-Columbian America.
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 Cleveland Museum of Art 1940.499 · The Met 43.164 · The Met 55.111.56 +2
Coral also appears widely in Old World ornament and dress, e.g. The Met 43.164 (ca. 1690–1720, coral-bead embroidered robe), 55.111.56 (19th–first half 20th century, Algeria) and Cleveland 1916.272 (1800s, Siam); some records read "imitation coral", showing imitations coexisted with natural coral in ornament.
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 Cleveland Museum of Art 1940.499 · The Met 43.164 · The Met 55.111.56 +2
An early coral ornament in the catalogue is Cleveland 1940.499, a necklace (before 1532, Peru, coral), showing coral used as an ornamental material in pre-Columbian America. It thereafter appears widely in the Old World: The Met 43.164 (ca. 1690–1720, metal thread and coral beads on a statue robe), 55.111.56 (19th–first half 20th century, Algeria, silver, enamel and coral), 30.75.980 (19th century, Qing China, rank badge with pearls, coral and glass beads) and Cleveland 1916.272 (1800s, Siam, coral, pearl and silver beads with red lacquer). Some records read "imitation coral", showing imitations coexisted with natural coral in ornament.
Sources Cleveland Museum of Art 1940.499 · The Met 43.164 · The Met 55.111.56 +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
- Cleveland Museum of Art 1940.499coral
- The Met 43.164Metal thread, coral beads
- The Met 55.111.56Silver, enamel, coral
- Cleveland Museum of Art 1916.272coral, pearl, and silver beads covered with red lacquer
- The Met 30.75.980Pearls, coral and glass beads, and silk embroidery on silk satin
Cultural records for this material: Birthstone list.
How it is identified
Precious and common corals cannot be separated from imitations, dyed material or filled material by colour and appearance alone. Their identity is bound up with composition and structure — precious coral is biomineralised calcium carbonate that may be calcite or aragonite, and some pink-to-red look-alikes are dyed and impregnated aragonite of a different composition. Reliable identification therefore needs laboratory testing by a qualified gem laboratory.
Evidence grade AScope: Applies to precious and common corals; composition and structure calls require testing at a qualified gem laboratory.
Sources CIBJO Coral Blue Book 2024
Other research findings
Precious corals consist chiefly of calcium carbonate laid down by biological mineralization in aragonitic and/or calcitic structures; their gemmological properties stem essentially from this calcium carbonate (calcitic) makeup.
Evidence grade AScope: Applies to precious corals; some common corals such as black coral have non-calcareous skeletons and are excluded.
Sources CIBJO Coral Information Sheet
Precious corals belong only to three genera of the family Corallidae — Corallium, Pleurocorallium and Hemicorallium — and take a porcelain-like lustre once polished.
Evidence grade AScope: This is the CIBJO Coral Book trade classification, which may differ from the latest taxonomic nomenclature.
Sources CIBJO Coral Information Sheet
Coral quality factors differ by species, but size and uniform colour usually matter, especially in strands where matching is of primary importance; large, fine art carvings in rich pink to deep red are highly prized and very rare.
Evidence grade BScope: Describes precious coral in a trade association's reference guide; not a grading standard, not a statement about the value of any piece, and not a statement on whether any coral may be traded.
Sources CIBJO Retailers' Reference Guide (2021)
Limits of this research
- Research status: Formation, occurrence or other material-specific findings found in authoritative sources
- The cited source is a CIBJO information sheet for jewellery educators focused on classification, nomenclature and trade; it does not describe the physiologic mechanism by which polyps secrete and build the calcium carbonate skeleton (evidence gap).
- The source gives no numeric geological age for the formation of specific coral deposits, only organism growth and lifespan scales.
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
- Coral (confirm the coral group, scientific name, treatments and CITES status first)
GB/T 16552—2017 Table A.3 “Coral” · CIBJO Gemmological Laboratories Book 2024 §7.2.2.4 “Coral”
Construction or treatment status
Natural identity; treatment status unknown
Treatments recorded for this material: Dyed, Bleached, Filled / Fracture-filled, Coated, Waxed
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
Coral is often subjected to dyeing and bleaching. Under GB/T 16552-2017, dyeing counts as a treatment and must be stated in the name (§5.4.2.2 a); bleaching counts as an optimization, so the plain gem name may be used (§5.4.2.1 a). Do not assume it is unenhanced.
Evidence
- CIBJO · 5.78
What this means for you
Before buying, check the recommended listing name "Coral (confirm the coral group, scientific name, treatments and CITES status first)" 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
- Disclosure rules for the treatments above can change as authorities update their standards; re-check before relying on this page.
- Last reviewed
- 2026-09-01
Trade-name ruling
- Compliance review required before listing.
- Suggested listing name
- Coral (confirm the coral group, scientific name, treatments and CITES status first)
Care and wear
Care
care (cleaning)2 sources compared
Coral — care (cleaning): ultrasonic and steamer: 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, Coral row, CLEANING column (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (cleaning): Clean with soft leather and gentle brushing; do not use an ultrasonic cleaner, as the source counts coral among porous gems and says coral is especially vulnerable to ultrasonic cleaning.
CIBJO Coral Blue Book 2024
CIBJO Coral Book §6.2:special-care code g
- Treatment state
- any treatment state
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.1, p.22; §6.2 g, p.22 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (heat): It can crack if it loses structural water, so keep it away from heat and drying environments; it is prone to thermal shock, so do not expose it to extreme temperature changes.
CIBJO Coral Blue Book 2024
CIBJO Coral Book §6.2:special-care code c, special-care code d
- Treatment state
- any treatment state
- Applies only to
- some corals (the source does not say which)
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.2 c, d, p.22 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (light): Some colour-treated corals can fade or revert to their original colour; these should not be kept for long periods in strong natural light, strong artificial light or strong display lighting.
CIBJO Coral Blue Book 2024
- Treatment state
- colour treated
Source & check 2026-09-25
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.3, p.23 (locator checked 2026-09-22)
- Fact checked on
- 2026-09-25
Coral — care (light): Strong light can fade it or turn it back to its original colour, so do not wear it or leave it in such light for long periods.
CIBJO Coral Blue Book 2024
CIBJO Coral Book §6.2:special-care code e
- Treatment state
- any treatment state
- Applies only to
- some corals (the source does not say which)
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.2 e, p.22 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (chemicals): porous, so keep it away from coloured fluids; acids and solvents such as nail varnish remover dissolve it, so keep it away from every solvent and other strong chemicals.
CIBJO Coral Blue Book 2024
CIBJO Coral Book §6.2:special-care code b, special-care code f
- Treatment state
- any treatment state
- Applies only to
- some corals (the source does not say which)
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.2 b, f, p.22 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (chemicals): Changes made with dye, oil, resin, wax or plastic do not last, so keep it away from all solvents (dish-washing liquids included), chemicals and heat; coatings often come off easily with solvents, heat or abrasives, which usually harm the coral too, so keep it away from all of them.
CIBJO Coral Blue Book 2024
CIBJO Coral Book §6.2:special-care code h, special-care code k
- Treatment state
- treated
- Applies only to
- some corals (the source does not say which)
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.2 h, k, p.22–23 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (storage): When not being worn, store pieces of jewellery apart so they do not scratch one another.
CIBJO Coral Blue Book 2024
- Treatment state
- any treatment state
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.1, p.22 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (storage): As a biogenic gem, coral should be kept in conditions that are neither too dry nor too humid.
CIBJO Coral Blue Book 2024
CIBJO Coral Book §6.2:special-care code j
- Treatment state
- any treatment state
- Applies only to
- some corals (the source does not say which)
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.2 j, p.22–23 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (wear): Avoid rough handling
CIBJO Coral Blue Book 2024
- Treatment state
- any treatment state
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.1, p.22 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (wear): Corals are prone to scratching due to low hardness. Wear them with care.
CIBJO Coral Blue Book 2024
CIBJO Coral Book §6.2:special-care code a
- Treatment state
- any treatment state
- Applies only to
- some corals (the source does not say which)
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.2 a, p.22 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (re-cutting): coral with superficial colour or surface layers, and coated coral, should not be re-cut or re-polished.
CIBJO Coral Blue Book 2024
CIBJO Coral Book §6.2:special-care code i, special-care code k
- Treatment state
- treated
- Applies only to
- some corals (the source does not say which)
Source & check 2026-09-26
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §6.2 i, k, p.22–23 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (special care): orange and red coral assembled with polymers and dyed: special care (SC); avoid chemicals and solvents.
AGTA Gemstone Information Manual, 17th ed.
- Treatment state
- treated
- Only after these treatments
- dyeing, impregnation
Source & check 2026-09-26
- Source
- AGTA Gemstone Information Manual, 17th edition (August 2026) (AGTA): p.IX, Gemstone Information Chart, Coral Orange D,I / Red D,I, CARE REQUIRED / SPECIAL ADVICE (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — 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, Coral row, SETTING column (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (repair): polishing and thermal shock: use caution; jeweller's torch and pickle pot: avoid; note: it turns black or scorches in a torch flame and is attacked by 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, Coral row, REPAIR column (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — care (display): artificial light: relatively safe; heat in the display case and sunlight: use caution; note: avoid heat.
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, Coral 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 Coral, Martin's Gemstone Durability: Design to Display states for untreated Coral that ultrasonic and steam cleaning should be avoided, and the CIBJO Blue Book — Coral Book (Coral Commission 2024) states for Coral in any treatment state that it should not be cleaned ultrasonically. CIBJOThe CIBJO Blue Book — Coral Book (Coral Commission 2024) states, for any treatment state and only for some corals, that loss of structural water causes cracking, so keep it away from heat and dry conditions, as it is sensitive to thermal shock; under strong light it may fade or revert to its original colour, so do not wear or keep it under strong light for long; it is porous and dissolves on contact with acids and solvents (such as nail-polish remover), so keep it away from all solvents and other strong chemicals; and it is soft and scratches easily, so wear it with care. LightThe same Coral Book states for colour-treated Coral that some may fade or revert to the original colour and should not be left under strong light for long, and for treated Coral (only some corals) that dyeing, oiling, resin, wax or plastic impregnation are not permanent, so keep it away from all solvents, chemicals and heat. Martin, Gem DurabilityMartin's Gemstone Durability: Design to Display states for untreated Coral that prong, bezel and channel settings need care, and tension and pavé settings should be avoided.
This table scrolls sideways on narrow screens.
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.
untreated
- ultrasonic and steamer: avoid
- prong, bezel and channel: use caution; flush and pavé: avoid
- polishing and thermal shock: use caution; jeweller's torch and pickle pot: avoid; note: it turns black or scorches in a torch flame and is attacked by acids
- artificial light: relatively safe; heat in the display case and sunlight: use caution; note: avoid heat
any treatment state
- Clean with soft leather and gentle brushing; do not use an ultrasonic cleaner, as the source counts coral among porous gems and says coral is especially vulnerable to ultrasonic cleaning Coral Book §6.2 g
- some corals (the source does not say which): It can crack if it loses structural water, so keep it away from heat and drying environments; it is prone to thermal shock, so do not expose it to extreme temperature changes Coral Book §6.2 c, d
- some corals (the source does not say which): Strong light can fade it or turn it back to its original colour, so do not wear it or leave it in such light for long periods Coral Book §6.2 e
- some corals (the source does not say which): porous, so keep it away from coloured fluids; acids and solvents such as nail varnish remover dissolve it, so keep it away from every solvent and other strong chemicals Coral Book §6.2 b, f
- When not being worn, store pieces of jewellery apart so they do not scratch one another
- some corals (the source does not say which): As a biogenic gem, coral should be kept in conditions that are neither too dry nor too humid Coral Book §6.2 j
- Avoid rough handling
- some corals (the source does not say which): care (wear) Coral Book §6.2 a
colour treated
treated
- some corals (the source does not say which): Changes made with dye, oil, resin, wax or plastic do not last, so keep it away from all solvents (dish-washing liquids included), chemicals and heat; coatings often come off easily with solvents, heat or abrasives, which usually harm the coral too, so keep it away from all of them Coral Book §6.2 h, k
- some corals (the source does not say which): coral with superficial colour or surface layers, and coated coral, should not be re-cut or re-polished Coral Book §6.2 i, k
treated (Only after these treatments: dyeing, impregnation)
Treatments and identification leads
Registered treatmentsThe treatments registered for Coral are dyeing, filling, bleaching and coating. Dyeing and bleaching have the status colour treated, while filling and coating have the status treated. Values not givenStability and market prevalence for dyeing, filling, bleaching and coating are all shown as “—”, meaning the cited source gives no value, not “none”. Identification cluesIdentification leads: for dyeing, uneven colour distribution, colourant concentrated in fractures or surface pits, possible distinctive fluorescence of the dye under UV, and fading when wiped with solvents such as acetone or anhydrous ethanol; for filling, a lustre in filled areas that differs from the coral itself, possible gas bubbles, and long-wave UV fluorescence that mostly does not match the host; bleaching removes surface impurities to improve colour and appearance and is not easy to detect; for coating, abnormal surface lustre, partial peeling of the film, possible anomalous refractive index readings, and characteristic peaks of the coating in infrared and Raman spectra.
This table scrolls sideways on narrow screens.
| Treatment | Market frequency (CIBJO) | Stability (CIBJO) | GB/T 16552 category | JJA/AGL listing | Identification leads |
|---|---|---|---|---|---|
| dyeingStatus: colour treated | — | — | Treatment | — | See identification leads |
| fillingStatus: treated | — | — | Graded — see §5.4.1, Table 1 | filling (red, pink, white and others); filling with the same material (red, pink, white and others) | See identification leads |
| bleachingStatus: colour treated | — | — | Optimization | bleaching (white) | See identification leads |
| coatingStatus: treated | — | — | Graded — see §5.4.1, Table 1 | — | See identification leads |
| colouring (including coloured wax) | — | — | — | colouring (including coloured wax) (pink, red) | — |
| bleached black coral | — | — | — | bleached black coral (brownish yellow) | — |
Where each treatment acts (schematics): Dyed · Filled / Fracture-filled · Bleached · Coated
“—” means the cited source gives no value for that item, not “none”. Source: 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 Coral, the name register records "Precious coral" and "common coral", for which no restriction on use as a name is recorded (CIBJO Coral Blue Book 2024 §5.78; CITES Appendices 2026 CORALLIIDAE; CITES Appendices 2026 Interpretation 6; CITES Appendices 2026 ANTIPATHARIA; CITES Appendices 2026 SCLERACTINIA); 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).
Standard and listing namesThe GB/T 16552—2017 standard name for Coral is coral (Table A.3), and the suggested listing name is Coral (confirm the group, scientific name, treatment and CITES status first). Trade and mineralogical namesTrade names or synonyms include common coral and Precious coral; Precious coral is restricted to the three genera of the family Corallidae defined in the CIBJO Coral Blue Book 2024, and the related high-risk name “Coral / Precious Coral” must state the species and the compliance status of its source. Institution usageOn authority wording, CIBJO records Coral (CIBJO Gemmological Laboratories Book 2024); the FTC text on file has no wording for this name (checked); GIA and Gem-A are unchecked; bodies without a recorded wording show the English name Coral, which does not represent their position. Japanese namesThe GSJ (Japan) formal name is coral, written in Japanese. Candidate search termsThe form registered in the JJA/AGL gem name handbook 2025 is a transliteration and is used only as a candidate search term. Names in four languagesNames are registered in Simplified Chinese, Traditional Chinese, English (Coral) and Japanese. National standard namesIndia (BIS) writes it as Coral / Moonga (मूंगा), and imports must meet CITES requirements.
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 (3) | ||||
| Precious coralEnglish | narrower name (variety or subtype) | matched only once the condition is confirmed | no restriction recorded | CIBJO Coral Blue Book 2024 §5.78 |
| common coralEnglish | market name | matched automatically | no restriction recorded | CITES Appendices 2026 CORALLIIDAE; CITES Appendices 2026 Interpretation 6; CITES Appendices 2026 ANTIPATHARIA; CITES Appendices 2026 SCLERACTINIA; Note: Related high-risk name “Coral / Precious Coral”: corals differ in CITES status — in CORALLIIDAE only four species such as Corallium japonicum are listed, each with a country in brackets (Appendix III under Interpretation 6), whereas the orders ANTIPATHARIA and SCLERACTINIA are listed in Appendix II as a whole; the species and the legality of the source must be stated. |
| さんご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
- サンゴ／珊瑚
- Chinese formal name
- 珊瑚 (GB/T 16552—2017 Table A.3)
- Mineralogical name
- Biogenic skeletal material; composition depends on taxon (calcareous or organic)
- Trade names and synonyms
- Precious coral (narrower name (variety or subtype); conditional name) · common coral (market name)
Four-language names
- 简体中文
- 珊瑚
- 繁體中文
- 珊瑚
- English
- Coral
- 日本語
- コーラル／珊瑚
National and regional formal names
- India (BIS)
- Coral / Moonga (मूंगा); CITES compliance required for import
See also: Misleading and prohibited trade names · Supplementary name index
Classification
- Origin
- Natural materials
- Material domain
- Natural organic and biogenic materials
- Browsing family
- Coral 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.1In the “Coral” row of GB/T 16552—2017, Annex B, Table B.1, bleaching improves appearance and is an optimization; filling improves or changes durability and appearance, and coating improves or changes lustre, colour and other aspects of appearance, both being graded; dyeing improves or changes colour and is a 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, Coral in red, pink, white and other colours has an untreated tier, and filling and filling with the same material are recorded, both treated as filling; for pink and red Coral the original lists no untreated tier, and colouring (including coloured wax) is recorded, treated as dyeing and waxing; for white Coral the original lists no untreated tier, and decolouring is recorded, treated as bleaching; brownish-yellow Coral has an untreated tier and is recorded as decolourised from black coral, treated as bleaching.
GB/T 16552-2017, Annex B, Table B.1
Table B.1, row “Coral” (p.17):
This table scrolls sideways on narrow screens.
| Method | Effect | Category |
|---|---|---|
| Bleaching | Improves appearance | Optimization |
| Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| 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
This table scrolls sideways on narrow screens.
| Gem name | Species | Colour | Listed in the table | Notes |
|---|---|---|---|---|
| Coral | Coral | red, pink, white and others | an untreated tier is listed; filling (Filled / Fracture-filled); filling with the same material (Filled / Fracture-filled) | |
| Coral | Coral | pink, red | the source lists no untreated tier; colouring (including coloured wax) (Dyed, Waxed) | |
| Coral | Coral | white | the source lists no untreated tier; bleaching (Bleached) | |
| Coral | Coral | brownish yellow | an untreated tier is listed; bleached black coral (Bleached) |
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
Registered material facts for Coral: under the CIBJO trade definition (an organisation's handbook, not a national standard), the jewellery trade considers only a few species and species complexes of the family Corallidae, called precious coral (5.78). Composition is registered by class: calcareous coral consists mainly of inorganic (CaCO3) and organic components, while horny coral is almost entirely organic. Hardness is registered by class, Mohs hardness 3–4.5 for calcareous coral and 2–3 for horny coral; these are ranges for the whole class, not measurements of Coral itself. Density: calcareous coral 2.6–2.7 g/cm³ (worked out from the clause value 2.65 and tolerance ±0.05), horny coral 1.3–2.12 g/cm³ (worked out from the clause value 1.35 and tolerance +0.77, −0.05). Optic character is aggregate, and birefringence is not measurable on an aggregate. Refractive index: calcareous coral 1.48–1.66, horny coral 1.55–1.58 (worked out from the clause value 1.56–1.57 and tolerance ±0.01), both readings commonly obtained with the spot method, typical values rather than absolute limits. Untreated, the lustre is waxy, vitreous on polished surfaces.
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”.
Items below that name the class they cover give the cited clause’s value for that whole class, not a measurement of Coral (how to read class-level values).
Definition
Coral: collective name for thousands of marine colonial species of the phylum Cnidaria. A limited number of species, notably from the Anthozoa class, including many in the subclasses Alcyonaria (Octocorallia) and Hexacorallia, are suitable for use in decoration and adornment. For the jewellery industry, only a few species and species complexes of the Corallidae family, here called precious corals (5.78), are considered. Other species, both with calcium carbonate and/or keratinous exoskeletons, not used in jewellery but as decoration and trinkets are here called common corals (5.25). Jewellery grade coral lives in deep ocean and secrete biomineralized calcium carbonate to form a hard skeleton. The chemical composition of coral is calcium carbonate (82–87%) with minor magnesium. It can also include small amounts of calcium sulphate, iron oxide and various phosphates.
CIBJO Coral Blue Book 2024
- Qualification
CIBJO trade definition from an institutional manual, not a national standard. The English text quotes the full definition at §5.27 of the Coral Blue Book 2024.
Source & check 2026-09-25
- Source
- CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.27, p.13 (locator checked 2026-09-25)
- Fact checked on
- 2026-09-25
Coral — composition (chemistry): mainly inorganic (CaCO3) and organic components
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- calcareous coral
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — composition (chemistry): made up almost entirely of organic matter
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- horny coral
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Structure
Coral — structure (overall): calcareous coral: the inorganic part is a cryptocrystalline aggregate and the organic part is non-crystalline. Horny coral: non-crystalline.
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): §5.3.4 (locator checked 2026-09-22)
- Fact checked on
- 2026-09-22
Durability
Coral — Mohs hardness: 3–4.5
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
- calcareous coral
- Qualification
This is the range for the whole class, not a measured value for this variety. The clause gives two ranges that must not be merged and this entry falls under both; the other range is listed alongside it on the same page.
Source & check 2026-09-20
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-20)
- Fact checked on
- 2026-09-20
Coral — Mohs hardness: 2–3
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
- horny coral
- Qualification
This is the range for the whole class, not a measured value for this variety. The clause gives two ranges that must not be merged and this entry falls under both; the other range is listed alongside it on the same page.
Source & check 2026-09-20
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-20)
- Fact checked on
- 2026-09-20
Coral — 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): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — 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
- calcareous coral
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — stability: Hydrochloric acid has no effect on it
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- horny coral
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Physical properties
Coral — density: 2.6–2.7 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- calcareous coral
- Qualification
The clause we cite gives 2.65, with a stated tolerance of ±0.05. The range shown here is worked out from that.
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — density: 1.3–2.12 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- horny coral
- Qualification
The clause we cite gives 1.35, with a stated tolerance of +0.77 / -0.05. The range shown here is worked out from that.
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Optical
Coral — 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): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — refractive index: 1.48–1.66
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- calcareous coral
- 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): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — refractive index: 1.55–1.58
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- horny coral
- 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. The clause we cite gives 1.56–1.57, with a stated tolerance of ±0.01. The range shown here is worked out from that.
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — 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): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — 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): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — fluorescence (overall): white coral: none to strong, blue-white; light pink / orange-red to red coral: from none to orange-red, orange-pink-red; deep red coral: from none to dark red, dark violet-red.
GB/T 16553—2017
UV fluorescenceblue-whitenone–strong, white coralfrom none to: orange-redorange-pink-redlight pink / orange-red to red coralfrom none to: dark reddark violet-reddeep red coralDots are illustrative colours built from the colour names, not measured values
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- calcareous coral
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — fluorescence (overall): generally none
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- horny coral
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — spectrum (UV-visible): pink-to-red calcareous coral: characteristic absorption peak.
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): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — spectrum (infrared): Diagnostic mid-IR bands differ by coral type: calcareous coral's come from carbonate-ion vibration, horny coral's from vibrating functional groups (radicals) in protein and other organic matter.
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): §5.3.4 (locator checked 2026-09-22)
- Fact checked on
- 2026-09-22
Coral — magnification: along the length, parallel bands that differ slightly in colour and transparency, wave-like structure, in cross-section, concentric layering together with a radial structure.
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- calcareous coral
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — magnification: on the longitudinal surface the outer layer sometimes looks pimpled, in cross-section, concentric layers or tree-ring-like rings.
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- horny coral
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
body colour2 sources compared
Coral — body colour: Precious corals are those that are used in jewellery and decoration, specifically red, pink and white varieties with porcelain like lustre after polishing. They are limited to species belonging to the family Corallidae, consisting of the three following groups: Corallium, Pleurocorallium and Hemicorallium.
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- untreated
- Qualification
In chapter 7 of the CIBJO Gemmological Laboratories Book, the colour descriptions of Rhodochrosite, Rhodonite, Ruby and other entries also name red or a reddish colour.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Coral — body colour: light pink red to dark red, orange red (pink), white and yellow.
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- calcareous coral
- Qualification
In chapter 5 of GB/T 16553—2017, the colour entries of Rhodochrosite, Natural Conch Pearl / Natural Melo Pearl, Prehnite and other variety clauses also name red or a reddish colour.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Coral — body colour: black, golden yellow and yellow brown
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- horny coral
- Qualification
In chapter 5 of GB/T 16553—2017, the colour entries of Epidote, Cassiterite, Turtle Shell and other variety clauses also name black or a blackish colour.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Quality factors
Coral — quality factor (lustre): waxy; polished surfaces take a vitreous lustre.
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): §5.3.4 (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): 1.57 / 2; Closest values: 1Ivory 1.535 / 1.85, 2Black Coral 1.565 / 1.71, 3Mammoth Ivory 1.53 / 1.75, 4Chrysocolla 1.516 / 2.2, 5Apophyllite 1.536 / 2.4
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
- Alterations
any change made to corals or artificial products that requires general (5.45) or specific (5.91) information.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.3, p.10
- Artificial coral
misnomer for an imitation with no known natural counterparts.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.6, p.11
- Blue coral
reef-building coral, a common coral, of calcareous composition belonging to the family Helioporidae (subclass Octocorallia), specially the Heliopora coerulea. It has a distinct blue colour, with a rough and porous skeleton that usually requires resin impregnation to be used as ornament. Note — see Clause 2 Normative References; Convention on International Trade in Endangered Species of Wild Fauna and Flora.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.13, p.11
- Common coral
common corals of both calcareous and non-calcareous types are not considered as “precious coral” and some may be found in coral reefs. Includes species from the Isidae, Primonidae, Zoanthidae, Helioporidae, Melithaeidae, Sylasteridae families and Antipatharia order. It is not used in the jewellery industry. Note — For additional information regarding “Precious coral” see clauses 5.78 and 5.27, and the annexes.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.25, p.13
- Cultured
the term “cultured” shall only be applied to “cultured pearls”. Note — See the CIBJO Pearl Book for additional information.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.28, p.14
- Gem
another term, often used as an adjective, to describe an exceptional coral or other gemstone noting perfection or very high quality. See gemstone clause 5.44. Note — the term “Gem” shall only be used to qualify the terms “real”, “precious”, “genuine” and “natural”.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.43, p.15
- Imitation of coral
artificial products that only simulate the appearance of coral.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.51, p.16
- Invertebrate
an animal without an internal backbone. Examples include cnidarians (e.g. reef corals, precious corals, sea fans), molluscs (e.g. snails, clams), arthropods (e.g. insects, spiders, shrimp), echinoderms (e.g. starfish, sea urchins) and annelids (e.g. worms).
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.53, p.16
- Lace coral
common coral belonging to the Stylaster genus (Sylasteridae family), with similar visual characteristics to some pink to red precious corals but with a different composition (biomineralized aragonite). Usually dyed and impregnated. Note — see Clause 2 Normative References; Convention on International Trade in Endangered Species of Wild Fauna and Flora.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.56, p.16
- Lustre enhancement
any treatment, other than polishing, applied to enhance the lustre of a coral.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.58, p.17
- Reef coral
Reef building corals that live in shallow water in specific ecosystems (e.g. Great Barrier Reef, Caribbean). Not considered precious corals and not used the jewellery industry.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.82, p.20
Weights, grading sieves and pricing
- Carat (ct)
a unit of weight, one carat being equivalent to 0.2 g (200 milligrams or 1/5 gram).
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.17, p.12
- Gram
the gram (g) is 1/1000 of a kilogram, a unit of mass of the International System of Units.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.49, p.16
- Kan
a unit of weight equal to 1,000 momme or 3.75 kilogram. This unit was most frequently applied by the Japanese coral industry.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.54, p.16
- Kin
a unit of weight equal to 600 gram. This unit was most frequently applied by the Japanese and Taiwanese coral industry.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.55, p.16
- Momme
unit of weight, equal to 0.13 ounces or 3.75 gram; 1,000 momme = 1 kan. This unit was most frequently applied by the Japanese coral industry, sometimes spelt monme.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.64, p.18
- Weight
mass of a diamond, gemstone, coral, pearl or cultured pearl, synthetic stone and other artificial products. Note — The SI (Système International) generally uses the term mass instead of weight. Mass is a measure of an object’s inertial property, or the amount of matter it contains. Weight is a measure of the force exerted on an object by gravity or the force needed to support it.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.101, p.21
Appearance and quality descriptors
- Body colour
the dominant, overall colour of coral.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.14, p.12
- Colour
colour has three attributes: hue, tone, and saturation. Hue is the basic impression of colour -yellow, green, blue, etc. Tone is the relative impression of lightness or darkness of the colour. Saturation is the strength or intensity of the colour. In general, the colour of precious coral may be described in terms of a combination of ‘body colour’ and colour distribution.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.22, p.13
- Lustre
The quality and quantity of light a coral reflects from its surface, being usually porcelanous with a variable degree of glassy appearance.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.57, p.17
Fashioning, drilling and cleaning
- Carving
an object or design cut from a hard material as an artistic work.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.19, p.12
- Cleaning
to leave corals in a mixture of water and hydrogen peroxide (5%) for a couple of days to bring the pigment back to its original colour. Cleaning is considered a normal lapidary practice (5.69).
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.20, p.12
- Cut
the style or shape in which coral and artificial products have been fashioned.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.29, p.14
- Cutting
one of several normal lapidary practices (5.69) used to give a shape to corals.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.30, p.14
- Drilled
a coral with a cylindrical hole engineered to enter at one point and exit on the opposite side. Also see part-drilled (5.75).
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.35, p.14
- Part-Drilled
a coral with a cylindrical hole engineered to enter at one point but which does not exit. Sometimes known as half-drilled.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.75, p.19
Trade roles and places
- Place of origin
name of the geographical origins where corals have been harvested, e.g., Mediterranean Sea, Atlantic Ocean, South China Sea, Sea of Japan and Pacific Ocean.
CIBJO Blue Book — Coral Book (Coral Commission 2024) (CIBJO): §5.77, p.19
Entries in the source that only point to another clause: Simulant (§5.89, p.20) → §5.51 Imitation of coral
Definitions are quoted verbatim from the cited CIBJO Blue Book; […] marks an excerpt, and the full definition is at the cited clause.
Testing and market
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: §6.2.4.
How far testing can go
Coral 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 in surface hollows; under long- and short-wave UV lamps the dye may fluoresce in an uncharacteristic way; wiping with acetone or absolute ethanol can lift the colour; Raman and UV-visible spectra separate pink-red calcareous coral from dyed coral.
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): §5.3.4 (dyeing) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral that has undergone filling can be identified by the following features: Under magnification the surface luster of the filled part differs from that of the coral itself and gas bubbles may be present in the filled area; under long-wave UV the filled part mostly fluoresces differently from the rest of the coral; infrared spectra show characteristic absorption bands of the filler; luminescence imaging (such as a UV fluorescence viewer) shows how the filler is distributed.
GB/T 16553—2017
- Treatment state
- treated
- Does this standard apply
- can be followed as a reference only
- Treatment
- filling
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (filling) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral that has undergone bleaching can be identified by the following features: removes impurities from the surface layer to improve the colour and appearance; hard to detect.
GB/T 16553—2017
- Treatment state
- colour treated
- Does this standard apply
- can be followed as a reference only
- Treatment
- bleaching
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (bleaching) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral 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 in places; refractive index readings may be abnormal; infrared and Raman spectra show characteristic peaks of the film.
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): §5.3.4 (coating) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Coral — 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
Coral — notes on test methods in the CIBJO laboratory protocol:
| Test method | What the protocol notes for it |
|---|---|
| Microscope: | Thermal reaction test |
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
Coral has a clause-level definition registered in the CIBJO Gemmological Laboratories Book 2024 under the term Coral; the cross-check result is a direct CIBJO definition, also present in the GB/T annex. The CIBJO wording is quoted in full under Clause-level definitions on this page.
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| Term | Clause | Definition | Cross-check |
|---|---|---|---|
| Coral | 7.2.2.4 | Corals are marine invertebrates. Cnidarians with skeletons are referred to collectively as “coral”. Precious corals are those that are used in jewellery and decoration, specifically red, pink and white varieties with porcelain like lustre after polishing. They are limited to species belonging to the family Corallidae, consisting of the three following groups: Corallium, Pleurocorallium and Hemicorallium. Coral mainly consists of calcite or aragonite and may contain organic pigments. Descriptions of precious coral species can be found in the CIBJO Coral Book. Distinction criteria | Defined directly by CIBJO; also present in the GB/T annex. |
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 Coral Book (Blue Book), 2024.
- CITES Secretariat. Appendices I, II and III, valid from 5 March 2026.
Further reading
Recorded cultural contexts
Japan's JJA 2021 revised roster lists Coral for March. This records trade-association convention only; it does not establish material identity, natural origin, treatment, provenance, or effect.
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| Publisher or holder | Region | From / period | Source and locator |
|---|---|---|---|
| Japan Jewellery Association | Japan | from 20 December 2021 | Tanjoseki (Japanese birthstone roster, Japan Jewellery Association page; revision of 20 December 2021) 2021 revised birthstone roster, March row: Coral |
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 Coral on this site: 12 entries listed by this site's parent-entry links; synthetic, treated and similar entries carry their recorded state after the name; this page (Coral) is marked.
- Coral
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| Page | Content | Status |
|---|---|---|
| Browsing family | Coral materials | Live |
| Treatments recorded for this material | Dyed, Bleached, Filled / Fracture-filled, Coated, Waxed | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Coral 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.