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Natural organic and biogenic materials · Organic or biogenic material · Natural identity; treatment status unknown
Calcareous Coral
One of the two types of coral distinguished when identifying coral under GB/T 16553: composed mainly of inorganic matter (calcium carbonate) plus organic matter. Colour, hardness, density, refractive index and other values are given separately for this type.
This page compares how the major standards and institutions name it, what must be disclosed when selling it, whether it can be worn every day, how it is treated and identified, and which source each conclusion comes from. Price, rarity and origin are outside the scope of this wiki.
What this page can answer
This page covers
- How Calcareous Coral forms and what gives its colourFormation setting, process and timescale, each finding graded and sourced
- How to identify Calcareous CoralIdentification points from the research literature
- Hardness, density and refractive index of Calcareous CoralEach value with its source and check date
- Calcareous Coral 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 Calcareous CoralThe 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
Calcareous coral is a class of coral defined by skeletal composition: mainly calcium carbonate with some organic matter, as opposed to the organic-matter-dominated 'horny (non-calcareous) coral'. It is a biogenic material: coral polyps secrete biomineralized calcium carbonate to form a hard skeleton, crystallizing as calcite or aragonite. Coral is made up chiefly of calcium carbonate (about 82–87%) plus a little magnesium; traces of calcium sulphate, iron oxide and assorted phosphates can also be present, and its gemmological behaviour is governed mainly by that (calcitic) calcium carbonate. Most common corals are calcareous and live on coral reefs. This record does not present any specific coral's facts as exclusive to 'calcareous coral'. GB/T 16553 is a nomenclature/identification standard whose full text is unavailable, and no clause numbers are relied on for the formation content.
Scope: Applies to explaining the composition, biogenic origin and common occurrence of calcareous coral as a class of corals 'with a predominantly calcium carbonate skeleton'; not applicable to determining the specific species, locality, treatment or value from the name.
Sources CIBJO Coral Blue Book 2024 · CIBJO Coral Information Sheet
Where it forms
Reef setting: common corals are mostly of the calcareous type and occur in coral reefs.
Sources CIBJO Coral Blue Book 2024 · CIBJO Coral Information Sheet
Marine setting: corals are marine invertebrates that secrete calcium carbonate skeletons.
Sources CIBJO Coral Blue Book 2024 · CIBJO Coral Information Sheet
How it forms, step by step
Coral polyps (a colony) grow.
Sources CIBJO Coral Blue Book 2024 · CIBJO Coral Information Sheet
They secrete biomineralized calcium carbonate to form a hard skeleton, crystallizing as calcite or aragonite.
Sources CIBJO Coral Blue Book 2024 · CIBJO Coral Information Sheet
After harvesting and working, the skeleton is used as ornament/gem material; the specific species and any treatment require identification.
Sources CIBJO Coral Blue Book 2024 · CIBJO Coral Information Sheet
Link to appearance
It appears as a relatively dense coral skeleton made mainly of calcium carbonate; but appearance cannot substitute for identifying the species and the calcareous/non-calcareous category.
Sources CIBJO Coral Blue Book 2024 · CIBJO Coral Information Sheet
Timescale
The cited sources give no absolute age or growth duration for calcareous coral.
Sources CIBJO Coral Blue Book 2024 · CIBJO Coral Information Sheet
Related base materials
- Coral: A class of coral defined by skeletal composition (calcareous skeleton); a classification name, not a mineral species
Supporting findings
Calcareous coral is a biogenic material: coral polyps secrete biomineralized calcium carbonate that hardens into a skeleton, crystallizing as calcite or aragonite; the gemmological properties of precious corals derive essentially from their (calcitic) calcium carbonate composition.
Evidence grade AScope: A biogenic-process statement; it does not confirm whether a given sample is calcitic or aragonitic.
Sources CIBJO Coral Information Sheet · CIBJO Coral Blue Book 2024
Common corals are mostly of the calcareous type and occur in coral reefs; the occurrence of calcareous coral relates to shallow-water reef environments.
Evidence grade AScope: Occurrence of common (calcareous) corals; precious calcareous corals are deep-water species, and this record does not conflate the two.
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.
Seas and coasts
- Mediterranean SeaCorallium rubrum, found mostly in the Mediterranean
Sources CIBJO Coral Blue Book 2024
- Atlantic coasts of North Africa, Spain and Portugal
Sources CIBJO Coral Blue Book 2024
- Waters off JapanPleurocorallium elatius
Sources CIBJO Coral Blue Book 2024
- Waters off Taiwan, ChinaPleurocorallium elatius
Sources CIBJO Coral Blue Book 2024
- Waters off Hawaii, United States
Sources CIBJO Coral Blue Book 2024
- Midway Seamount
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 the origin determination guide and the overview of recorded localities.
How it is identified
The appearance of calcareous-coral can be imitated, so appearance alone cannot confirm it. Imitation coral lacks the chemical composition, physical properties or structure of natural coral; identification requires laboratory methods — examining internal features such as the different polished lustre of filled fissures at 10× magnification, together with instrumental testing of chemistry and structure — while dyed, filled, impregnated and coated treatments must be detected and disclosed at sale. Limitations: some treatments and imitations are visible only under magnification or instrumentation, and the conclusion must be issued by an accredited gemological laboratory through testing rather than inferred from appearance.
Evidence grade AScope: Identification and separation points; testing must be performed by an accredited gemological laboratory, and no self-test thresholds are given.
Sources CIBJO Coral Blue Book 2024 · CIBJO Gemstone Book 2022
Other research findings
Calcareous coral is a class of coral defined by skeletal composition (mainly calcium carbonate with some organic matter), as opposed to the organic-matter-dominated horny (non-calcareous) coral; it is a material-classification name, not a mineral species.
Evidence grade BScope: A classification/identity-boundary judgement; the full text of GB/T 16553 could not be obtained, so the conclusion that depends on it could not be checked against the standard and no clause of it is cited.
Sources CIBJO Coral Information Sheet · CIBJO Coral Blue Book 2024
The calcareous coral skeleton is mainly calcium carbonate; the overall chemical composition of coral is calcium carbonate (about 82–87%) with minor magnesium.
Evidence grade AScope: Composition of calcareous coral as a broad class; exact proportions of a given species/sample require testing.
Sources CIBJO Coral Blue Book 2024
Limits of this research
- Research status: Formation, occurrence or other material-specific findings found in authoritative sources
- Calcareous coral is a material-classification name (mainly calcium carbonate skeleton), not a mineral species; no specific species/sample is confirmed.
- The full text of GB/T 16553 could not be obtained, so no clause of it is cited and the conclusion that depends on it could not be checked against the standard.
- Precious calcareous corals are deep-water species, distinct in ecology from shallow-water reef corals, and this record does not conflate them.
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
- Calcareous coral (state the variety and any treatments)
GB/T 16553—2017 §5.3.4.3 · CIBJO Gemmological Laboratories Book 2024 §7.2.2.4 “Coral”
Construction or treatment status
Natural identity; treatment status unknown
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
Calcareous Coral's material identity has open questions that are not fully settled; this site lists it as "Calcareous coral (state the variety and any treatments)" pending further verification.
Evidence
- GB/T · §5.3.4.3
What this means for you
Before buying, check the recommended listing name "Calcareous coral (state the variety and any treatments)" and any disclosed treatments on this page, and ask the seller for a grading report if in doubt.
Known uncertainty
- This entry's exact material identity is not fully settled.
- See “Disclosure and cautions” above
- Last reviewed
- 2026-09-26
Care and wear
No care facts are recorded for this entry itself. Its parent material has care records: see Coral.
VerifyNames, standards, technical facts, clauses and sources
Names
Standard and listing namesThe Chinese standard name for Calcareous Coral is calcareous coral (GB/T 16553—2017), and the suggested listing name is Calcareous Coral (stating the variety and treatment). Trade and mineralogical namesUnder GB/T 16553—2017, the mineralogical name refers to coral composed mainly of calcium carbonate with some organic matter. Names in four languagesNames are registered in Simplified Chinese, Traditional Chinese, English (Calcareous Coral) and Japanese (pending verification); the Japanese name shown is the entry's own and is pending verification, and the wording used by the GSJ (Japan) for this name is not yet verified by this site. Institution usageOn the wording of GIA, FTC, CIBJO and Gem-A, the FTC and CIBJO texts on file have no wording for this name (checked), and GIA and Gem-A are unchecked; bodies without a recorded wording show the entry's own English name, Calcareous Coral, which does not represent their position.
- GSJ (Japan) formal name
- 石灰質サンゴ（待核） (not yet checked for this body — the entry's own Japanese name is shown)
- Chinese formal name
- 钙质珊瑚 (GB/T 16553—2017 §5.3.4.3)
- Mineralogical name
- Calcareous coral: coral made mainly of calcium carbonate with some organic matter (GB/T 16553 §5.3.4.3)
Four-language names
- 简体中文
- 钙质珊瑚
- 繁體中文
- 鈣質珊瑚
- English
- Calcareous Coral
- 日本語
- 石灰質サンゴ（待核）
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
What it is and how it's identified
Calcareous Coral consists mainly of inorganic calcium carbonate together with organic components; GB/T 16553—2017 registers calcareous coral and horny coral separately. Mohs hardness is 3–4.5; site note: hardness alone is not enough to judge durability. Density is 2.6–2.7 g/cm³; site note: the cited clause's original value is 2.65 with a stated tolerance of ±0.05, and the range is worked out from that. Refractive index is 1.48–1.66; site note: this is the reading commonly obtained with the spot method under the cited clause, a typical value, not an absolute limit. Untreated Calcareous Coral has a body colour of light pink to deep red, orange-red (pink), white, yellow and similar colours; site note: the cited clause also lists golden yellow, yellowish brown and other yellows for horny coral, so calcareous and horny coral must be told apart by composition, and the clause states that calcareous coral effervesces with hydrochloric acid while horny coral does not react.
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”.
Durability
Calcareous 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
- General note
- hardness only, not durability
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
Physical properties
Calcareous Coral — density: 2.6–2.7 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- 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 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Optical
Calcareous Coral — refractive index: 1.48–1.66
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- Qualification
The clause we cite gives this as a value commonly read by the spot (distant-vision) method. It is a common value, not an absolute limit.
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.3.4 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Calcareous Coral — body colour: light pink to deep red, orange-red (pink), white, yellow and other colours.
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- Qualification
The clause we cite also lists yellow shades (golden yellow, yellowish brown) for horny coral, and the two classes are told apart by composition: the same clause says calcareous coral effervesces with hydrochloric acid while horny coral does not react.
- 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
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 / 2.65; Closest values: 1Scapolite 1.558 / 2.67, 2Changhua Stone 1.56 / 2.6, 3Amethyst 1.548 / 2.67, 4Balin Stone 1.56 / 2.55, 5Qingtian Stone 1.565 / 2.77
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
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.
- AQSIQ / SAC (China). GB/T 16553—2017 Gems — Testing.
- SAMR / SAC (China). GB/T 16552—2017 Gems — Nomenclature.
- CIBJO – The World Jewellery Confederation. The Coral Book (Blue Book), 2024.
- eCFR (United States). 16 CFR Part 23 — Guides for the Jewelry, Precious Metals, and Pewter Industries.
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 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 (Calcareous Coral) is marked.
- Coral
Sub-entries (11)
This table scrolls sideways on narrow screens.
| Page | Content | Status |
|---|---|---|
| Browsing family | Coral materials | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Calcareous 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. The entry exists so that buyers and sellers can check naming, disclosure and material facts item by item.