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UnderstandWhat it is, what people ask, how far this page goes
Natural inorganic gem materials · Rock / mineral aggregate · Natural identity; treatment status unknown
Agate
Also known asBeihong Agate (conditional name)
A banded aggregate of chalcedony, i.e. cryptocrystalline quartz with banded structure; GB/T 16552-2017 Table A.2 lists it on the same line as Chalcedony and Jasper. 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 Agate
Every sentence below is followed by the registered fact it rests on; answers add no new facts and promise no outcome.
Q1Can agate be dyed, and can you tell dyed agate by its colour?
Agate's colour can come from dyeing or heating, and its colour and banding do not reveal whether the hue is natural, so appearance cannot settle whether it has been treated.G&G Summer 2014 · CIBJO Gemstone Book 2022A trustworthy treatment ruling calls for instrumental examination at a qualified gem laboratory.G&G Summer 2014 · CIBJO Gemstone Book 2022For dyed agate, CIBJO notes that the colour may fade or revert to its original colour in strong light.CIBJO Gemstone Book 2022Whether one particular bead is natural, treated or synthetic — only a laboratory report can settle that.What this page can answer
Q2How do you know a piece is genuine agate and not glass or resin?
Appearance alone cannot settle it: a trustworthy identification of agate calls for instrumental examination at a qualified gem laboratory.G&G Summer 2014 · CIBJO Gemstone Book 2022Agate is a cryptocrystalline quartz aggregate with concentric layers, zones or bands, a fibrous and granular texture, and sometimes small crystal-lined cavities.GB/T 34098—2017Polished surfaces commonly show a vitreous lustre, and fracture surfaces a greasy or waxy lustre.GB/T 34098—2017Whether one particular bead is natural, treated or synthetic — only a laboratory report can settle that.What this page can answer
Q3How does agate get its bands?
Under the prevailing view, silica-rich fluids reach voids in volcanic rock through microfissures or infiltration canals.G&G Fall 2013The shape, width and overall pattern of the bands depend on silica concentration, temperature, pressure and the timing of each influx of fluid.G&G Fall 2013At the final stage, quartz crystals of various colours, including amethyst and smoky quartz, may grow in the centre of the void.G&G Fall 2013At Sidi Rahal in Morocco, agate growth continued over millions of years, in successive stages.G&G Fall 2013
Q4What colours does agate come in, and what causes them?
Agate is commonly red, yellow, grey, white or green, and some pieces combine several colours.GB/T 34098—2017Its colour runs in curved or angular bands or layers, while landscape, picture, moss and dendritic agate show other coloured patterns or branching inclusions.CIBJO Gemmological Laboratories Book 2024The source's literature summary says iron, titanium and manganese affect only the colour of each band.G&G Fall 2013In agate from Sidi Rahal, Morocco, the red and brown-red bands are coloured by iron compounds such as hematite and goethite.G&G Fall 2013
Q5What is agate, and how is it related to chalcedony and quartz?
Agate is mainly banded chalcedony, which is fibrous microcrystalline quartz, a microcrystalline variety of silica that also contains other silica polymorphs.G&G Fall 2013Its mineral phase is recorded as quartz.CIBJO Gemmological Laboratories Book 2024Agate is found in volcanic as well as sedimentary host rocks.G&G Fall 2013
Q6Can agate fade in the sun?
Dyed agate can: for dyed agate, CIBJO notes that the colour may fade or revert to its original colour in strong light, and advises not wearing or leaving it in strong light for long periods.CIBJO Gemstone Book 2022
Q7What makes a good-quality agate?
CIBJO's reference guide for retailers, which records what collectors favour rather than a grading standard, says unusual banding or landscape-like scenes are particularly prized, as are agates with striking dendritic inclusions.CIBJO Retailers' Reference Guide (2021)Iris agate and fire agate showing strong iridescent colours are also collected.CIBJO Retailers' Reference Guide (2021)
Q8What does agate symbolize, and does it have healing powers?
There is no scientific evidence that agate 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)Museum evidence places one of the earliest datable uses of agate or carnelian as beads at about 2900–2350 BCE, an Indus-style bead from Mesopotamia, with later examples from Middle Kingdom Egypt, Kassite Mesopotamia and Minoan Crete.The Met 59.41.42 · The Met 25.3.252 +4
Sources cited in these answers ASA/CAP guidance (UK)
What this page can answer
This page covers
- How Agate 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 AgateIdentification points from the research literature; how far lab testing can go
- Treatments and enhancements of AgateThe enhancements and treatments the GB/T and JJA/AGL tables list
- Caring for and wearing AgateCleaning, heat, chemicals and light, as the cited sources give them
- Hardness, density and refractive index of AgateEach value with its source and check date
- Agate 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 AgateHow people have used it, with museum objects
- Listing and disclosing AgateThe listing name to use; what must be disclosed before sale
- Standard clauses that define AgateWhich 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
- Chalcedony bands (colours schematic)
- Centre idiomorphic quartz, if present (colours vary)
- Void / vesicle (not to scale)
If you reuse this animation, please credit LumaLark Wiki and link to this pageLicense: CC BY 4.0
Scene-by-scene transcript (8 scenes, with evidence grades and sources)
The caption of each scene in the animation above, with its evidence grade and sources.
Scene 1What agate is
Agate is a silica aggregate composed mainly of fibrous microcrystalline quartz, i.e. macroscopically banded chalcedony — the banded form of chalcedony — also containing other silica polymorphs (moganite, opal-CT).
The G&G 2013 source focuses on basalt-hosted Sidi Rahal agate; other modes of occurrence (e.g. sedimentary) are not detailed.
Scene 2One possible origin of the cavity: vesicles in lava
Cavities such as the basalt geodes that host agate can begin as vesicles in lava: as a lava flow cools, bubbles of gas or steam expand while the rock solidifies, leaving small rounded cavities called vesicles; when minerals deposited from solutions circulating through the rock later fill them, the fillings are called amygdules.
Scope: The general origin of vesicles and amygdules (the source describes lavas of Isle Royale, Lake Superior, where all vesicles have since been filled and converted to amygdules); how agate actually fills such cavities is covered by other entries in this record.
Evidence grade AScene 3Prevailing hypothesis: fluid enters and fills the void from rim to centre
Most workers hold that silica-rich fluids reach volcanic voids through microfissures or infiltration canals and fill them in rim-to-centre cycles; how the bands look is set by silica concentration along with temperature, pressure and the timing of each influx.
Scope: Described as the prevailing hypothesis; banding genesis is still debated.
Scope: The exact mechanism of rhythmic banding is not fully understood.
Evidence grade AScene 4Final stage: idiomorphic quartz may grow in the centre
At the final stage, idiomorphic quartz of various colours (including amethyst and smoky quartz) may grow in the void centre, sometimes with calcite, hematite and barite.
Scene 5Where agate occurs: volcanic and sedimentary rocks
Its host rocks span volcanic and sedimentary types.
Scene 6Example: the reduced lower tier of the Cordillera Flow
in the southern Paraná Volcanic Province, along the Brazil–Uruguay border, world-class agate-geode and amethyst-geode deposits occur in the reduced lower tier of the Cordillera Flow (deposits in Artigas, Uruguay); according to the source, reducing and acidic hot water formed these agate and amethyst deposits.
Scene 7Example: Sidi Rahal agate
In the Moroccan example (Sidi Rahal), agates are lens-shaped nodules up to 25 cm within Triassic basaltoids; red/brown-red bands are coloured by Fe compounds (hematite, goethite), and Fe³⁺-rich silica fluids are thought to have induced crystallization, which lasted millions of years and proceeded in stages.
Agate growth at Sidi Rahal continued over millions of years, in successive stages.
Evidence grade AScope: An inference by the authors based in part on moganite; not precise dating.
Scene 8What you end up seeing
the centre may hold colourless or coloured quartz, and no two specimens are identical. Colour varies by locality: at Sidi Rahal, Morocco, a red/brown-red band coloured by Fe compounds lies just inside a pink outer rim, interiors are often grey-blue/white, and in the centre white-grey chalcedony coexists with colourless quartz.
In brief: Agate is a silica aggregate composed mainly of fibrous microcrystalline quartz, i.e. macroscopically banded chalcedony — the banded form of chalcedony — also containing other silica polymorphs (moganite, opal-CT).
Full research record (formation summary, where it forms, 5 formation steps, link to appearance, timescale, related base materials, 1 supporting finding)
Agate is a silica aggregate composed mainly of fibrous microcrystalline quartz, i.e. macroscopically banded chalcedony — the banded form of chalcedony — also containing other silica polymorphs (moganite, opal-CT). Its host rocks span volcanic and sedimentary types. Most researchers hold that silica-rich fluids pass into volcanic voids via microfissures or infiltration canals and fill them rim-to-centre in repeated cycles; the shape and width of the bands and their overall pattern depend on the silica concentration together with temperature, pressure and the timing of the fluid pulses, whereas Fe, Ti and Mn are held to affect only the colour of the bands. At the final stage, idiomorphic quartz of different colours may grow in the void centre. In the Moroccan example (Sidi Rahal), agates are lens-shaped nodules up to 25 cm within Triassic basaltoids; red/brown-red bands are coloured by Fe compounds (hematite, goethite), and Fe³⁺-rich silica fluids are thought to have induced crystallization, which lasted millions of years and proceeded in stages.
Scope: Used to explain the origin of banded chalcedony (agate) as a filling of voids in volcanic rock and the source of its colour bands, with Sidi Rahal, Morocco, as the case study; details may differ for other localities and modes of occurrence (e.g. fissure or sedimentary).
Sources G&G Fall 2013
Where it forms
Voids/vesicles in volcanic rock (geodes, vugs): under the prevailing hypothesis, silica-rich fluids enter through microfissures or infiltration canals and fill them cyclically as bands.
Sources G&G Fall 2013
Sedimentary rocks: beyond volcanic settings, agate also occurs in various sedimentary rocks.
Sources G&G Fall 2013
Post-magmatic hydrothermal and hypogenic settings: hematite and goethite probably formed under post-magmatic hydrothermal conditions; Cu sulfides, Ti oxides, calcite and other solid inclusions were incorporated under post-magmatic hydrothermal or hypogenic conditions.
Sources G&G Fall 2013
Example: in the southern Paraná Volcanic Province, along the Brazil–Uruguay border, world-class agate-geode and amethyst-geode deposits occur in the reduced lower tier of the Cordillera Flow (deposits in Artigas, Uruguay); according to the source, reducing and acidic hot water formed these agate and amethyst deposits.
Sources Brazilian Journal of Geology
How it forms, step by step
Under the prevailing hypothesis, silica-rich fluids are believed to reach the volcanic void via microfissures or infiltration canals.
Under the prevailing hypothesis, fluids fill the void cyclically from rim to centre, precipitating fibrous microcrystalline quartz (chalcedony) as successive concentric bands.
Band shape, width and overall pattern depend on silica concentration, temperature, pressure and timing of fluid influxes; the source's literature summary says Fe, Ti and Mn affect only the colour of each band, though the same paper links Sidi Rahal agate crystallization to Fe³⁺-rich fluids.
At the final stage, idiomorphic quartz of various colours (including amethyst and smoky quartz) may grow in the void centre, sometimes with calcite, hematite and barite.
At Sidi Rahal, crystallization is thought to have been induced by Fe³⁺-rich silica fluids; red/brown-red bands are coloured by Fe compounds such as hematite; crystallization lasted millions of years and proceeded in stages.
Link to appearance
Banded patterns, which may form concentric multi-layer bands or landscape, stalactite or pipe-shaped patterns; the centre may hold colourless or coloured quartz, and no two specimens are identical. Colour varies by locality: at Sidi Rahal, Morocco, a red/brown-red band coloured by Fe compounds lies just inside a pink outer rim, interiors are often grey-blue/white, and in the centre white-grey chalcedony coexists with colourless quartz.
Sources G&G Fall 2013
Timescale
Sidi Rahal agate crystallization lasted millions of years and proceeded in stages; the moganite-to-low-quartz transformation generally lowers moganite content over tens of millions of years, and moganite content has been proposed as an age-evaluation tool, though it shows no direct correlation with the geological age of the host rock.
Sources G&G Fall 2013
Related base materials
- Chalcedony: banded form | Agate is the banded form of chalcedony
- Quartz / Silica (SiO₂): mineral-group | Composed mainly of fibrous microcrystalline quartz
Supporting findings
Agate is found in volcanic as well as sedimentary host rocks; Sidi Rahal (Morocco) agates are lens-shaped nodules up to 25 cm within Triassic basaltoids, with a pink outer rim composed of opal-CT.
Evidence grade AScope: Uses Sidi Rahal as the case study; other deposits differ in scale and host rock.
Recorded localities
Authoritative sources list the localities below; the list is not exhaustive.
Africa
- MadagascarMost famous gems
- Sidi Rahal, Atlas Mountains, Morocco
Asia
- IndiaMost famous gems
South America
- BrazilMost famous gems
Seas and coasts
- WorldwideOccurs in nearly all countries
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
At Sidi Rahal, Morocco, the red/brown-red agate bands are coloured by Fe compounds (hematite, goethite); crystallization is thought to have been induced by Fe³⁺-rich fluids, the agates occurring as lens-shaped geode-filling nodules in basalt.
Evidence grade AScope: Concerns only the Fe-bearing red/brown-red layers of the Sidi Rahal samples; it does not address the origin of colourless or grey-blue layers, nor other localities.
Human use and museum objects
Museum evidence places one of the earliest datable uses of agate/carnelian as beadwork at ca. 2900-2350 BCE (Met 59.41.42, an Indus-style bead from Mesopotamia), recurring in Middle Kingdom Egypt (25.3.252, 15.3.538), Kassite Mesopotamia (1994.433) and Minoan Crete (26.31.258).
Evidence grade AScope: Applies to collection objects recorded as agate or carnelian (chalcedony/quartz parent material); natural versus heat-induced colour is not distinguished in the records.
Sources The Met 59.41.42 · The Met 25.3.252 · The Met 1994.433 +3
- The Metropolitan Museum of Art — Bead (59.41.42)
- The Metropolitan Museum of Art — Sweret Bead (25.3.252)
- The Metropolitan Museum of Art — Bead with cuneiform inscription of Kurigalzu I or II (1994.433)
- The Metropolitan Museum of Art — Carnelian bead (26.31.258)
- The Metropolitan Museum of Art — Gold and banded agate earring (74.51.3937)
- Cleveland Museum of Art — Fragment of a Necklace (1915.15)
The Met holds a carnelian (chalcedony/agate) bead in Indus-Valley style, ca. 2900-2350 BCE, recorded from Mesopotamia (acc. 59.41.42), among the earliest in the collection. From Egypt come a Dynasty 11 "sweret" bead (acc. 25.3.252, ca. 2051-1981 B.C., Thebes) and Middle Kingdom-early New Kingdom strings of carnelian beads (acc. 15.3.538, ca. 1981-1295 B.C., Memphite Region). A Kassite agate bead bearing a cuneiform inscription (Kurigalzu I or II; acc. 1994.433, ca. 14th century BCE) comes from Mesopotamia. Minoan carnelian beads (acc. 26.31.258, ca. 1650-1500 BCE) and Roman gold-and-banded-agate earrings (acc. 74.51.3937, 2nd century CE) show continuity in the Aegean and Mediterranean. Agate is the banded form of chalcedony; this evidence pertains to the chalcedony/quartz parent material, and the museum material fields that distinguish "carnelian" and "agate" both fall under it.
Sources The Met 59.41.42 · The Met 25.3.252 · The Met 1994.433 +3
- The Metropolitan Museum of Art — Bead (59.41.42)
- The Metropolitan Museum of Art — Sweret Bead (25.3.252)
- The Metropolitan Museum of Art — Bead with cuneiform inscription of Kurigalzu I or II (1994.433)
- The Metropolitan Museum of Art — Carnelian bead (26.31.258)
- The Metropolitan Museum of Art — Gold and banded agate earring (74.51.3937)
- Cleveland Museum of Art — Fragment of a Necklace (1915.15)
Scope: A museum object evidences only the existence and date of that artefact itself; it does not establish widespread ancient use of the material, nor does it attest the origin, naturalness, or treatment of any modern specimen.
Objects cited
- The Met 59.41.42Carnelian
- The Met 25.3.252Carnelian
- The Met 1994.433Agate
- The Met 26.31.258Carnelian
- The Met 74.51.3937Gold, banded agate
- Cleveland Museum of Art 1915.15steatite, glass, carnelian, and faience
How it is identified
For agate, colour and banding by themselves do not reveal whether the hue is natural or produced by dyeing or heating, so visual appearance cannot settle naturalness or treatment; a trustworthy identification and any treatment ruling call for instrumental examination at a qualified gem laboratory, and this entry is no basis for self-testing.
Evidence grade AScope: Appearance cannot replace identification; naturalness, dyeing or heat treatment must be determined at a qualified gem laboratory, and this entry is not a self-testing basis.
Sources G&G Summer 2014 · CIBJO Gemstone Book 2022
Other research findings
Agate is mainly banded chalcedony (fibrous microcrystalline quartz), a microcrystalline variety of silica that also contains other silica polymorphs.
Evidence grade AScope: Defines agate's composition and the banded-chalcedony definition; dyed/heated material excluded.
Agate is a banded chalcedony, and among chalcedonies unusual banding or landscape scenes are particularly prized, as are agates with dramatic dendritic inclusions; iris agate and fire agate with strong iridescent colours are also collected.
Evidence grade BScope: What collectors favour, as described in a trade association's reference guide; not a grading standard and not a statement about the value of any piece.
Sources CIBJO Retailers' Reference Guide (2021)
Limits of this research
- Research status: Formation, occurrence or other material-specific findings found in authoritative sources
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
- Agate
GB/T 16552—2017 Table A.2 “Chalcedony(Agate/Jasper)” · CIBJO Gemmological Laboratories Book 2024 §7.2.1.3 “Agate”
Construction or treatment status
Natural identity; treatment status unknown
Treatments recorded for this material: Dyed, Heated / Heat-treated, Filled / Fracture-filled
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
Agate is often subjected to dyeing. Under GB/T 16552-2017, dyeing counts as an optimization, so the plain gem name may be used (§5.4.2.1 a). Do not assume it is unenhanced.
What this means for you
Before buying, check the recommended listing name "Agate" 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
- Industry-wide term that does not denote a single species.
- Suggested listing name
- Agate
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
Agate — 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
- Applies only to
- other colours, sold under a colour prefix
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Agate — care (special care): dyed: normal care.
AGTA Gemstone Information Manual, 17th ed.
- Treatment state
- treated
- Only after these treatments
- dyeing
Source & check 2026-09-26
- Source
- AGTA Gemstone Information Manual, 17th edition (August 2026) (AGTA): p.VIII, Gemstone Information Chart, Chalcedony Agate D, CARE REQUIRED / SPECIAL ADVICE (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
Care of Agate: the CIBJO Gemstone Book (2022) states, for dyed agate of other colours named with a colour prefix, that it may fade or revert to its original colour in strong light, so do not wear or leave it in strong light for extended periods. The American Gem Trade Association (AGTA) Gemstone Information Manual, 17th edition, states that dyed agate needs only normal care.
This table scrolls sideways on narrow screens.
| Question | Matching entries |
|---|---|
| Light and display | other colours, sold under a colour prefix: may fade or revert to its original colour in strong light; do not wear or leave it in strong light for extended periods |
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 |
|---|---|---|---|---|---|
| Heating | — | — | Optimization | — | — |
| Filling | — | — | Graded — see §5.4.1, Table 1 | — | — |
| Dyeing | — | — | Optimization | — | — |
| 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 Chalcedony); 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 Agate, the name register records "Agate" and "Beihong Agate", for which no restriction on use as a name is recorded (GB/T 16552 revision draft for comment (2023, not in force) Table A.2; GB/T 16552—2017 no occurrence of “Beihong Agate” in the full text); 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 formal name for Agate is listed in the "Chalcedony (Agate/Jasper)" row of Table A.2; the suggested listing name is "Agate". Names in four languagesThe four-language names cover Simplified Chinese, Traditional Chinese, English (Agate) and Japanese (the GSJ formal name). Trade and mineralogical namesThe trade name and synonym is Agate, and the mineralogical name is banded chalcedony (microcrystalline quartz); Germany (RAL) writes Achat and the EU writes Agate. Institution usageOn authority wording, CIBJO lists Agate (CIBJO Gemmological Laboratories Book 2024); the FTC text has no wording for this name (checked), and GIA and Gem-A have not been checked; bodies without a recorded wording show the entry's own English name, which does not represent their position. Trade and mineralogical namesGB/T 34098—2017 Table A.1 places trade names such as aventurine quartz, Huanglong jade and Nanhong in one group shared by agate, quartzite jade, chalcedony and jasper, and the text does not say which name corresponds to which variety. Candidate search termsBeihong Agate (and its Chinese counterpart) rests on the draft revision of GB/T 16552 issued for comment (2023, not in force) and serves only as a candidate search term.
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) | ||||
| AgateEnglish | market name | matched automatically | no restriction recorded | editorial ruling (no clause cited) |
| Beihong AgateEnglish | transliteration | search candidate only | no restriction recorded | GB/T 16552 revision draft for comment (2023, not in force) Table A.2; GB/T 16552—2017 no occurrence of “Beihong Agate” in the full text; Note: Draft standard for comment, not in force. |
| 北红玛瑙Simplified Chinese | narrower name (variety or subtype) | search candidate only | no restriction recorded | GB/T 16552 revision draft for comment (2023, not in force) Table A.2; GB/T 16552—2017 the name does not occur anywhere in the text; Note: Draft standard for comment, not in force. |
How each authority words this name: see Names › Authority wording.
- GSJ (Japan) formal name
- アゲート／瑪瑙
- Chinese formal name
- 玛瑙 (GB/T 16552—2017 Table A.2, row “Chalcedony(Agate/Jasper)”)
- Mineralogical name
- Banded chalcedony (microcrystalline quartz)
- Trade names and synonyms
- Beihong Agate (transliteration; conditional name)
Four-language names
- 简体中文
- 玛瑙
- 繁體中文
- 瑪瑙
- English
- Agate
- 日本語
- アゲート／瑪瑙
National and regional formal names
- Germany (RAL)
- Achat
- European Union
- Agate
GB/T 34098 trade names
GB/T 34098-2017 Table A.1 lists these trade names in one cell shared by agate and quartzite jade, chalcedony, jasper; the original does not say which name goes with which: 东陵石 Dongling Shi, 黄龙玉 Huanglong Yu, 南红 Nanhong, 密玉 Mi Yu, 阿拉善玉 Alashan Yu, 通天玉 Tongtian Yu, 台山玉 Taishan Yu, 大别山玉 Dabieshan Yu, 贺州玉 Hezhou Yu, 鸡血玉 Jixue Yu, 金丝玉 Jinsi Yu, 南红玛瑙 Nanhong Manao, and others.
The full table and naming rule are on the Quartzose Jade page.
See also: Misleading and prohibited trade names · Supplementary name index
Classification
- Origin
- Natural materials
- Material domain
- Natural inorganic gem materials
- Browsing family
- Quartz and chalcedony materials
- Identity tier
- Rock / mineral aggregate
- Mineral chemical class
- Silicates
- Construction or treatment status
- Natural identity; treatment status unknown
Treatments listed by standards
GB/T 16552-2017, Annex B, Table B.1
Table B.1, row “Chalcedony (Agate/Jasper)” (p.16):
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| Method | Effect | Category |
|---|---|---|
| Heating | Improves or changes colour | Optimization |
| Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Dyeing | Improves or changes colour | Optimization |
What Table B.1 is, and how the “see 5.4.1” grades are defined: see the GB/T 16552: optimization vs treatment page.
JJA/AGL (Japan) table of principal gem names, 2025
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| Gem name | Species | Colour | Listed in the table | Notes |
|---|---|---|---|---|
| Agate | Quartz | banded | 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.11
How to read the JJA/AGL table: see the Gem treatments page.
What it is and how it's identified
Agate is composed of quartz; its structure is a cryptocrystalline quartz aggregate with concentric layers, rings or bands, fibrous or granular, and cavities (geodes) are sometimes seen. Under the GB/T 16553—2017 clause for chalcedony (including agate and jasper, the whole class), Mohs hardness is 5–7, cleavage none, density 2.5–2.77 g/cm³, optic character anisotropic aggregate, and birefringence not measurable on an aggregate; refractive index is 1.535–1.539, and since the clause has finer ranges, this site uses the overall value. For chalcedony as a whole class, an optical effect (iridescence) may be seen, as may chatoyancy; GB/T 34098—2017 records that agate sometimes shows iridescence. Untreated Agate usually shows vitreous lustre on polished surfaces and greasy or waxy lustre on fractures. Iridescent agate is translucent with iridescent colours; fire agate is mostly opaque.
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”.
Chemical composition, luminescence, UV-visible spectrum, infrared spectrum, magnification: these whole-class features are given in the cited clause for chalcedony, including agate and jasper (the whole class), so they are not repeated on the Agate page; see the material facts on the Chalcedony entry.
Items below that name the class they cover give the cited clause’s value for that whole class, not a measurement of Agate (how to read class-level values).
Definition
Agate — composition (phase): quartz
CIBJO Gemmological Laboratories Book 2024
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Structure
Agate — structure (overall): a cryptocrystalline quartz aggregate with concentric layers, zones or bands. The texture is fibrous and granular. Small crystal-lined cavities (druses) are sometimes visible.
GB/T 34098—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-17
- Source
- GB/T 34098—2017 Quartzose jade — Classification and nomenclature (GB/T): §5.3 (locator checked 2026-09-17)
- Fact checked on
- 2026-09-17
Durability
Agate — Mohs hardness: 5–7
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
- chalcedony, including agate and jasper (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Agate — cleavage: none
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chalcedony, including agate and jasper (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Physical properties
Agate — density: 2.5–2.77 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chalcedony, including agate and jasper (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Optical
Agate — optic character: anisotropic aggregate
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chalcedony, including agate and jasper (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Agate — refractive index: 1.535–1.539
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chalcedony, including agate and jasper (the whole class)
- General note
- the clause has finer ranges
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Agate — birefringence: not measurable on an aggregate
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chalcedony, including agate and jasper (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Agate — transparency: Iris agate is translucent, with iridescent colours; Fire agate is largely opaque.
CIBJO Gemmological Laboratories Book 2024
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Agate — pleochroism: not measurable on an aggregate
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- chalcedony, including agate and jasper (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
optical effect (iridescence)2 sources compared
Agate — optical effect (iridescence): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chalcedony, including agate and jasper (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Agate — optical effect (iridescence): Iridescence is sometimes visible
GB/T 34098—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-17
- Source
- GB/T 34098—2017 Quartzose jade — Classification and nomenclature (GB/T): §5.3 (locator checked 2026-09-17)
- Fact checked on
- 2026-09-17
Agate — optical effect (chatoyancy): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chalcedony, including agate and jasper (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Agate — magnification: banding, ring-like zoning or concentric layering, tiny quartz crystals occasionally seen in the gaps between bands or inside cavities.
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.5 Magnification (locator checked 2026-09-28)
- Fact checked on
- 2026-09-26
Agate — body colour: Chalcedony with curved or angular bands or layers, also called banded agate; chalcedony with other coloured patterns or dendritic inclusions may be called landscape agate, picture agate, moss agate and dendritic agate, respectively. Iris agate is translucent, with iridescent colours; Fire agate is largely opaque, with iridescent colours against a brown body colour.
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- untreated
- Qualification
In chapter 7 of the CIBJO Gemmological Laboratories Book, the colour descriptions of Smoky Quartz, Morion / very dark Smoky Quartz, Sunstone and other entries also name brown or a brownish colour.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Agate — common colours: red, yellow, grey, white, green and similar colours, and combinations of several colours.
GB/T 34098—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- Qualification
Among the quartzose jade varieties in GB/T 34098—2017, Quartzite Jade, Chalcedony, Jasper and other varieties also name red or a reddish colour among their common colours; the standard separates these varieties by crystallinity and by whether they show silica-replacement pseudomorphs.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- GB/T 34098—2017 Quartzose jade — Classification and nomenclature (GB/T): §5.3 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
- CIBJO definitions
- chatoyancy
Quality factors
Agate — quality factor (lustre): Polished surfaces commonly show a vitreous luster. Fracture surfaces commonly show a greasy or waxy luster.
GB/T 34098—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
Source & check 2026-09-20
- Source
- GB/T 34098—2017 Quartzose jade — Classification and nomenclature (GB/T): §5.3 (locator checked 2026-09-17)
- Fact checked on
- 2026-09-20
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
This material (RI / SG midpoints): 1.537 / 2.63; Closest values: 1Amethyst 1.548 / 2.67, 2Charoite 1.554 / 2.66, 3Changhua Stone 1.56 / 2.6, 4Shoushan Stone 1.56 / 2.7, 5Balin Stone 1.56 / 2.55
Show the full chart (330 registered materials)
Outside the full chart's range, drawn as triangles at the edge (RI / SG midpoints): Hematite 3.045/5.12, Synthetic Rutile 2.76/4.26, Rutile 2.753/4.23, Synthetic Moissanite 2.67/3.22
Testing and market
The CIBJO laboratory protocol covers Agate under “Chalcedony” (§6.1.16): see identification on the Chalcedony entry; the required tests are listed on the CIBJO laboratory protocol table for Chalcedony.
How far testing can go
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
Clause-level definitions
Agate is defined directly in the CIBJO Gemmological Laboratories Book 2024 under the entry name Agate, as chalcedony whose bands or layers are curved or angular; it is also known as banded agate. Cross-check result: defined directly by CIBJO; also present in the GB/T annex.
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| Term | Clause | Definition | Cross-check |
|---|---|---|---|
| Agate | 7.2.1.3 | Chalcedony with curved or angular bands or layers, also called banded agate; chalcedony with other coloured patterns or dendritic inclusions may be called landscape agate, picture agate, moss agate and dendritic agate, respectively. Iris agate is translucent, with iridescent colours; Fire agate is largely opaque, with iridescent colours against a brown body colour | 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.
- AQSIQ / SAC (China). GB/T 34098—2017 Quartzose jade — Classification and nomenclature.
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 Quartz on this site: 74 entries listed by this site's parent-entry links; synthetic, treated and similar entries carry their recorded state after the name; this page (Agate) is marked.
- Quartz
Sub-entries (57)
- Agate
Sub-entries (1)
- Amethyst
- Ametrine
- Aventurine Quartz
- Aventurine Quartz / Green Aventurine
- Banded Agate
- Black Agate
- Bloodstone / Heliotrope
- Blue Lace Agate
- Carnelian
- Chalcedony
Sub-entries (2)
- Chrysoprase
- Citrine
- Clear Quartz / Rock Crystal
- Coated Quartz
- Colourless to White Quartz (brand name: Azeztulite)
- Crazy Lace Agate
- Dendritic Agate
- Dyed Agate (Treated: dyed)
- Elestial Quartz / Skeletal Quartz
- Eye Agate
- Flower Agate / Cherry Blossom Agate
- Green Quartz
- High-clarity quartz with golden needle-like inclusions
- Included Quartz
- Jasper
Sub-entries (1)
- Madeira Citrine
- Malachite Agate
- Morion / very dark Smoky Quartz
- Moss Agate
- Moss Chalcedony
- Multi-inclusion Quartz
- Onyx (banded chalcedony)
- Phantom Quartz
- Prase
- Prasiolite / Green Quartz
- Quartz Cat’s-eye
- Quartz claimed to be from the Himalayas
- Quartz Crystal
- Quartz with dark needle-like inclusions
- Quartz with fine fibrous inclusions
- Quartz with flower-like inclusions
- Quartz with golden needle-like inclusions
- Quartz with green needle-like inclusions
- Quartzite Jade
- Quartzose Jade
- Red Agate
- Rock Crystal
- Rose Quartz
- Rutilated Quartz
- Sard
- Sardonyx
- Silicified Asbestos
Sub-entries (2)
- Hawk’s Eye
- Tiger’s Eye
Sub-entries (1)
- Smoky Quartz
- Smoky Quartz (brown variety)
- Strawberry Quartz
- Yellow-green Quartz
- Agate
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| Page | Content | Status |
|---|---|---|
| Browsing family | Quartz and chalcedony materials | Live |
| Treatments recorded for this material | Dyed, Heated / Heat-treated, Filled / Fracture-filled | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Agate 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.