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UnderstandWhat it is, what people ask, how far this page goes
Natural inorganic gem materials · Mineral / gemstone variety · Natural identity; treatment status unknown
Alexandrite Cat’s-eye
A Chrysoberyl variety showing both colour change and a cat's-eye effect, listed in GB/T 16552—2017 Table A.1 as "alexandrite cat's-eye". 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 Alexandrite Cat’s-eye 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 Alexandrite Cat’s-eyeIdentification points from the research literature; how far lab testing can go
- Treatments and enhancements of Alexandrite Cat’s-eyeThe enhancements and treatments the GB/T and JJA/AGL tables list
- Hardness, density and refractive index of Alexandrite Cat’s-eyeEach value with its source and check date
- Alexandrite Cat’s-eye 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 Alexandrite Cat’s-eyeThe listing name to use; what must be disclosed before sale
- Standard clauses that define Alexandrite Cat’s-eyeWhich 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
Cat's-eye alexandrite is the chrysoberyl (BeAl2O4) variety that shows both a colour change and a cat's-eye. As an alexandrite it is green in daylight and brownish/purplish red under incandescent light, while parallel needle-like inclusions (almost all rutile) give it a cat's-eye line under cabochon cutting. Hence a cat's-eye chrysoberyl that also shows a colour change is cat's-eye alexandrite. The two effects arise separately: the eye from needle scattering plus cabochon focusing, and the colour change from the mineral's light-source-dependent selective absorption; they are independent and can combine.
Scope: Covers chrysoberyl showing both colour change and the cat's-eye effect; for a single effect (colour change only or cat's-eye only), refer to the record for the corresponding variety.
Sources G&G Summer 2025 · GIA Alexandrite Description · GIA Emerald Description
Where it forms
Be-bearing systems such as granitic pegmatites, where chrysoberyl both hosts exsolved needle inclusions and shows light-source-dependent colour change.
Sources G&G Summer 2025
How it forms, step by step
Chrysoberyl crystallises in a Ti- and Cr-bearing system.
Sources G&G Summer 2025 · GIA Alexandrite Description
On cooling, titanium exsolves as rutile needles, providing the basis for the cat's-eye.
Sources G&G Summer 2025 · GIA Alexandrite Description
The crystal also absorbs light selectively, changing colour with the source; both effects combine in one crystal.
Sources G&G Summer 2025 · GIA Alexandrite Description
Link to appearance
Cat's-eye alexandrite combines a cat's-eye line with light-source-dependent colour change, one of the most prized chrysoberyl varieties.
Sources G&G Summer 2025 · GIA Alexandrite Description
Timescale
Needle inclusions exsolve on post-crystallisation cooling; the colour change is a solid-state property with no separate timescale.
Sources G&G Summer 2025
Related base materials
- Chrysoberyl: Mineral parent: this variety belongs to the mineral species chrysoberyl (BeAl2O4)
Causes of colour and optical effects
A cat's-eye chrysoberyl that also shows a colour change is cat's-eye alexandrite, a chrysoberyl variety combining both effects.
Evidence grade AScope: Defines the variety where the eye and colour change combine.
The cat's-eye forms as parallel needle inclusions (almost all rutile in chrysoberyl) scatter and focus the light beam.
Evidence grade AScope: Describes the cat's-eye (scatter/focus) mechanism.
The colour change is caused by light-source-dependent selective absorption, independent of the cat's-eye mechanism.
Evidence grade AScope: The two effects have different origins and can combine.
Sources GIA Alexandrite Description
How it is identified
Colour-change cat's-eye combines a colour shift with a cat's-eye effect, and materials that look alike may differ entirely in composition. Appearance cannot establish its identity, genesis or treatment status; an accredited laboratory must judge it after instrumentally testing composition, spectra and internal features, and no self-identification method is given here.
Evidence grade AScope: Colour-change cat's-eye identification must be determined by an accredited laboratory; no self-service method is given.
Sources CIBJO Gemstone Book 2022
Other research findings
Cat's-eye alexandrite is a variety of chrysoberyl (BeAl2O4), not a beryl-group mineral.
Evidence grade AScope: Belongs to the chrysoberyl family and must not be confused with the beryl family.
Sources G&G Summer 2025 · GIA Emerald Description
Limits of this research
- Research status: Only partial material-specific findings found; gaps are stated as gaps
- Chromophore details (Cr3+) of cat's-eye alexandrite are not directly given in the available sources.
- Synthetic cat's-eye alexandrite and origin determination are outside the formation scope.
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
- Alexandrite Cat's-eye
GB/T 16552—2017 Table A.1 “Alexandrite Cat’s-eye” · IMA Mineral List 2026-07 “Chrysoberyl”
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
Alexandrite Cat’s-eye is Chatoyant colour-change chrysoberyl; use "Alexandrite Cat's-eye" for listings, and disclose any known treatments.
Evidence
- GB/T · Table A.1, row 变石猫眼 (Alexandrite Cat’s-eye)
What this means for you
Before buying, check the recommended listing name "Alexandrite Cat's-eye" and any disclosed treatments on this page, and ask the seller for a grading report if in doubt.
Known uncertainty
- Last reviewed
- 2026-09-01
How lab reports word it
Report wording for Alexandrite Cat’s-eye is set out under report wording on the Alexandrite entry.
VerifyNames, standards, technical facts, clauses and sources
Names
The name register below lists one name for Alexandrite Cat’s-eye in a non-Latin script: 1 with no restriction recorded on use as a name.
Standard and listing namesThe Chinese formal name for Alexandrite Cat’s-eye is taken from GB/T 16552—2017 Table A.1, and the suggested listing name is likewise Alexandrite Cat’s-eye; a synonym, colour-change chrysoberyl cat’s-eye, is also recorded on the basis of GB/T 16552—2017. Trade and mineralogical namesThe mineralogical name is Chatoyant colour-change chrysoberyl. Names in four languagesNames are given in four languages: Simplified Chinese, Traditional Chinese, English (Alexandrite Cat’s-eye) and Japanese. The wording of Japan's GSJ is not yet verified by this site; the entry's own Japanese name is a katakana transliteration of Alexandrite Cat’s-eye. Institution usageOn authority wording, the FTC has been checked and its text on file has no wording for the name Alexandrite Cat’s-eye; whether GIA, CIBJO and Gem-A use this name is not yet verified; where a body has not recorded the name, the entry's own English name is shown, and this does not represent that body's position.
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 (1) | ||||
| 变色金绿宝石猫眼Simplified Chinese | synonym | matched automatically | no restriction recorded | GB/T 16552—2017 5.3.3 |
How each authority words this name: see Names › Authority wording.
- GSJ (Japan) formal name
- アレキサンドライト・キャッツアイ (not yet checked for this body — the entry's own Japanese name is shown)
- Chinese formal name
- 变石猫眼 (GB/T 16552—2017 Table A.1)
- Mineralogical name
- Chatoyant colour-change chrysoberyl
Four-language names
- 简体中文
- 变石猫眼
- 繁體中文
- 變石貓眼
- English
- Alexandrite Cat’s-eye
- 日本語
- アレキサンドライト・キャッツアイ
See also: Misleading and prohibited trade names · Supplementary name index
Classification
- Origin
- Natural materials
- Material domain
- Natural inorganic gem materials
- Browsing family
- Oxide minerals
- Identity tier
- Mineral / gemstone variety
- Mineral chemical class
- Oxides / hydroxides
- Construction or treatment status
- Natural identity; treatment status unknown
Treatments listed by standards
JJA/AGL designationsIn the November 2025 revision of the JJA/AGL Definitions and Nomenclature of Gemstones and Ornamental Materials, the list of main gemstone designations places Alexandrite Cat’s-eye, under the name Alexandrite Cat's Eye, beneath the species chrysoberyl, with colour green to bluish green and a separate no-treatment category. The notes record a distinct colour change to red to purplish red, and chatoyancy. See alsoHow to read the JJA/AGL table is explained on the Gem treatments 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 |
|---|---|---|---|---|
| Alexandrite Cat's Eye | Chrysoberyl | green to bluish green | an untreated tier is listed | distinct colour change to red to purplish red; chatoyancy |
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
Several material facts for Alexandrite Cat’s-eye are registered from the GB/T 16553—2017 clause values for "cat's-eye (chrysoberyl cat's-eye, the whole class)", not from data measured on Alexandrite Cat’s-eye alone: structure crystalline, orthorhombic; Mohs hardness 8–8.5; cleavage three directions, imperfect; optical character anisotropic, biaxial, positive; birefringence 0.008–0.01; both the cat's-eye effect and the colour-change effect can occur; density 3.71–3.75 g/cm³, where the site note explains that the cited clause gives 3.73 with a permitted tolerance of ±0.02 and the range is derived from the clause value and tolerance; refractive index 1.74–1.759, where the site note explains that the cited clause gives 1.746–1.755 with a permitted tolerance of +0.004/−0.006 and the range is derived from the clause value and tolerance; the site note adds that the clause has finer sub-ranges and the overall value is used.
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 chrysoberyl cat's-eye (the whole class), so they are not repeated on the Alexandrite Cat’s-eye page; see the material facts on the Cat’s-eye entry.
Items below that name the class they cover give the cited clause’s value for that whole class, not a measurement of Alexandrite Cat’s-eye (how to read class-level values).
Structure
Alexandrite Cat’s-eye — structure (overall): crystalline
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — structure (crystal system): orthorhombic
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — structure (crystal habit): tabular or granular; pseudo-hexagonal trilling twins
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Durability
Alexandrite Cat’s-eye — Mohs hardness: 8–8.5
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
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — cleavage: imperfect in three directions
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Physical properties
Alexandrite Cat’s-eye — density: 3.71–3.75 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
- Qualification
The clause we cite gives 3.73, with a stated tolerance of ±0.02. The range shown here is worked out from that.
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Optical
Alexandrite Cat’s-eye — optic character: biaxial, optically positive (anisotropic)
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — refractive index: 1.74–1.759
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
- Qualification
The clause we cite gives 1.746–1.755, with a stated tolerance of +0.004 / -0.006. The range shown here is worked out from that.
- General note
- the clause has finer ranges
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — birefringence: 0.008–0.01
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — pleochroism: weak trichroism: yellow, yellow-green and orange.
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — fluorescence (overall): weak to moderate, red
GB/T 16553—2017
UV fluorescenceredweak–moderateDots are illustrative colours built from the colour names, not measured values
- 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): §5.1.5 Fluorescence (locator checked 2026-09-28)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — optical effect (chatoyancy): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — optical effect (colour change): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Alexandrite Cat’s-eye — body colour: blue-green and purplish brown; rare
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- Qualification
In chapter 5 of GB/T 16553—2017, the colour entries of Zoisite, Sillimanite, Lazulite and other variety clauses also name green or a greenish colour.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 Colour · Alexandrite cat’s-eye (locator checked 2026-09-28)
- Fact checked on
- 2026-09-26
- CIBJO definitions
- chatoyancy, colour change
Quality factors
Alexandrite Cat’s-eye — quality factor (lustre): vitreous
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- chrysoberyl cat's-eye (the whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.5 (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): 1.749 / 3.73; Closest values: 1Cobalt Spinel 1.723 / 3.63, 2Grossular 1.745 / 3.9, 3Malachite 1.782 / 3.67, 4Rhodolite 1.755 / 3.9, 5Benitoite 1.78 / 3.65
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 Alexandrite Cat’s-eye under “Alexandrite” (§6.1.2): see identification on the Alexandrite entry; the required tests are listed on the CIBJO laboratory protocol table for Alexandrite.
The CIBJO laboratory protocol covers Alexandrite Cat’s-eye under “Chrysoberyl” (§6.1.18): see identification on the Chrysoberyl entry; the required tests are listed on the CIBJO laboratory protocol table for Chrysoberyl.
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
At the clause level, Alexandrite Cat’s-eye rests on GB/T 16552-2017 Annex A, where the term is Alexandrite Cat’s-eye and the definition summary reads Chatoyant colour-change chrysoberyl. The cross-check shows it is listed directly by GB/T, and CIBJO carries no standalone entry under the same name.
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| Term | Clause | Definition | Cross-check |
|---|---|---|---|
| Alexandrite Cat’s-eye | GB/T 16552-2017 Annex A | Chatoyant colour-change chrysoberyl | Listed directly by GB/T; CIBJO carries no standalone entry under the same name. |
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.
- RRUFF Project, in partnership with the IMA – International Mineralogical Association. IMA Mineral List.
- Geological Survey of Japan, AIST (Japan). Museum mineral specimens, browse by classification.
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.
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| Page | Content | Status |
|---|---|---|
| Browsing family | Oxide minerals | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Alexandrite Cat’s-eye 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.