On this page
UnderstandWhat it is, what people ask, how far this page goes
Natural inorganic gem materials · Mineral / gemstone variety · Natural identity; treatment status unknown
Bytownite
An intermediate-composition member of the plagioclase series, occasionally seen on the market as yellow to golden-brown crystals; the exact composition must be confirmed by testing. 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 Bytownite 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 BytowniteHow far lab testing can go
- Treatments and enhancements of BytowniteThe enhancements and treatments the GB/T and JJA/AGL tables list
- Hardness, density and refractive index of BytowniteEach value with its source and check date
- Bytownite in English, Chinese and Japanese; national standard namesNames in four languages, the GB/T standard name and the suggested listing name; and: Which of GIA, FTC, CIBJO and Gem-A have a name for it on record, and do those agree?
- Listing and disclosing BytowniteThe listing name to use; what must be disclosed before sale
- Standard clauses that define BytowniteWhich 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
Bytownite is a more calcic variety of the plagioclase solid-solution series defined by An content (about An70-90 by convention), more calcic than the adjacent labradorite; it is not an independent mineral species but a compositional-range name within the plagioclase continuous solid solution (albite NaAlSi3O8 - anorthite CaAl2Si2O8). Bytownite can occur in mafic volcanic and plutonic rocks: for example, sunstone phenocrysts in porphyritic basalt in Oregon have compositions around An67-72, right at the labradorite/bytownite boundary (Johnston 1991, who characterised the Ponderosa labradorite as being 70% anorthite with 30% albite, sitting right on the labradorite–bytownite divide); Ethiopian sunstone samples are mostly classified as labradorite, with only one spot giving bytownite. Like other plagioclase varieties, bytownite must be confirmed by the Ab-An-Or ternary diagram and compositional analysis.
Scope: Applies to the composition, occurrence and classification of natural bytownite as the name for a calcic range of the plagioclase series; does not cover artificially coloured (e.g. copper-diffused) material.
Sources G&G Fall 2013 · G&G Spring 2020 · G&G Summer 2025
- Oregon Sunstone: The Official State Gemstone of Oregon (Gems & Gemology, Fall 2013, Vol. 49, No. 3)
- Sunstone Plagioclase Feldspar from Ethiopia (Gems & Gemology, Spring 2020, Vol. 56, No. 1, Gem News International)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
Where it forms
Mafic volcanic rocks (porphyritic basalt): bytownite/labradorite phenocrysts can occur in porphyritic basalt.
Sources G&G Fall 2013 · G&G Spring 2020 · G&G Summer 2025
- Oregon Sunstone: The Official State Gemstone of Oregon (Gems & Gemology, Fall 2013, Vol. 49, No. 3)
- Sunstone Plagioclase Feldspar from Ethiopia (Gems & Gemology, Spring 2020, Vol. 56, No. 1, Gem News International)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
Plutonic and metamorphic rocks: calcic plagioclase occurs there and commonly hosts oriented needle-like iron oxide inclusions.
Sources G&G Fall 2013 · G&G Spring 2020 · G&G Summer 2025
- Oregon Sunstone: The Official State Gemstone of Oregon (Gems & Gemology, Fall 2013, Vol. 49, No. 3)
- Sunstone Plagioclase Feldspar from Ethiopia (Gems & Gemology, Spring 2020, Vol. 56, No. 1, Gem News International)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
How it forms, step by step
Calcic plagioclase (high An; bytownite composition about An70-90) crystallizes from calcium-rich mafic magma.
Sources G&G Fall 2013 · G&G Spring 2020 · G&G Summer 2025
- Oregon Sunstone: The Official State Gemstone of Oregon (Gems & Gemology, Fall 2013, Vol. 49, No. 3)
- Sunstone Plagioclase Feldspar from Ethiopia (Gems & Gemology, Spring 2020, Vol. 56, No. 1, Gem News International)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
In porphyritic basalt, bytownite/labradorite occurs as large phenocrysts in a finer-grained groundmass.
Sources G&G Fall 2013 · G&G Spring 2020 · G&G Summer 2025
- Oregon Sunstone: The Official State Gemstone of Oregon (Gems & Gemology, Fall 2013, Vol. 49, No. 3)
- Sunstone Plagioclase Feldspar from Ethiopia (Gems & Gemology, Spring 2020, Vol. 56, No. 1, Gem News International)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
Material near the labradorite/bytownite boundary must be classified by the Ab-An-Or ternary diagram and compositional analysis.
Sources G&G Fall 2013 · G&G Spring 2020 · G&G Summer 2025
- Oregon Sunstone: The Official State Gemstone of Oregon (Gems & Gemology, Fall 2013, Vol. 49, No. 3)
- Sunstone Plagioclase Feldspar from Ethiopia (Gems & Gemology, Spring 2020, Vol. 56, No. 1, Gem News International)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
Oriented needle-like iron oxide inclusions commonly develop in calcic plagioclase.
Sources G&G Fall 2013 · G&G Spring 2020 · G&G Summer 2025
- Oregon Sunstone: The Official State Gemstone of Oregon (Gems & Gemology, Fall 2013, Vol. 49, No. 3)
- Sunstone Plagioclase Feldspar from Ethiopia (Gems & Gemology, Spring 2020, Vol. 56, No. 1, Gem News International)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
Link to appearance
Bytownite is a calcic compositional range of the plagioclase series and can occur as large phenocrysts in porphyritic basalt. Neither the range name nor the appearance alone proves identity, which requires the Ab-An-Or ternary diagram and compositional analysis.
Sources G&G Fall 2013 · G&G Spring 2020 · G&G Summer 2025
- Oregon Sunstone: The Official State Gemstone of Oregon (Gems & Gemology, Fall 2013, Vol. 49, No. 3)
- Sunstone Plagioclase Feldspar from Ethiopia (Gems & Gemology, Spring 2020, Vol. 56, No. 1, Gem News International)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
Timescale
The sources give 40Ar/39Ar ages of about 15.51 ± 0.28 to 16.59 ± 0.10 Ma for the associated Oregon basalt eruptions (Miocene 15-17 Ma volcanism), the age of the host rock of bytownite/labradorite phenocrysts; no absolute duration for phenocryst crystallization itself is given.
Sources G&G Fall 2013 · G&G Spring 2020 · G&G Summer 2025
- Oregon Sunstone: The Official State Gemstone of Oregon (Gems & Gemology, Fall 2013, Vol. 49, No. 3)
- Sunstone Plagioclase Feldspar from Ethiopia (Gems & Gemology, Spring 2020, Vol. 56, No. 1, Gem News International)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
Related base materials
- Plagioclase solid-solution series (albite-anorthite): range-of | Bytownite is the name of a calcic range of the plagioclase solid-solution series, defined by An content
- Labradorite (adjacent range): adjacent-range | Bytownite is more calcic than labradorite; the two adjoin at about An70
Recorded localities
Authoritative sources list the localities below; the list is not exhaustive.
Africa
- Bushveld complex, South Africa
Sources Handbook of Mineralogy
North America
- Ottawa, Ontario, CanadaThe type material was later shown to be a mixture.
Sources Handbook of Mineralogy
- Near Lakeview, Lake County, Oregon, United States
Sources Handbook of Mineralogy
- Grants district, McKinley County, New Mexico, United States
Sources Handbook of Mineralogy
- Stillwater complex, Montana, United States
Sources Handbook of Mineralogy
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
Bytownite belongs to the plagioclase series, and any iridescence it may show shares labradorite's mechanism: solid-state exsolution forms alternating calcic and sodic submicron lamellae (the Bøggild intergrowth), calcic ones about 70–200 nm and sodic ones about 50–100 nm, with interference when adjacent thickness is on the order of a visible-light wavelength. Bytownite (about An70–90) is more calcic than labradorite and holds a larger share of calcic lamellae, so, arguably, this renders its lamellae thicker and the interference color longer in wavelength.
Evidence grade AScope: The cited sources record no iridescence example in the bytownite range; the family mechanism can be extended in principle, but strong labradorescence is placed at An46–60 in the sources, so this is a conservative mechanistic inference.
The cited sources place plagioclase with saturated labradorescence in the An46±2 to An60±2 range and note that the red iridescent zone is about 2–3 mol% more calcic than the blue one; because no iridescence example is given for the bytownite range, whether bytownite itself shows labradorescence is treated here only as a mechanistic inference, not as established fact.
Evidence grade BScope: An evidence-boundary note: bytownite's own iridescence is not documented by the sources.
Other research findings
Bytownite is a calcic variety of the plagioclase solid-solution series defined by An content, more calcic than the adjacent labradorite (about An70-90 by convention); it is not an independent mineral species.
Evidence grade BScope: A range-name statement; boundaries are conventional and the sources give only near-boundary composition examples.
Plagioclase phenocrysts (labradorite/bytownite composition) occur in highly porphyritic basalt in Oregon; their composition is about An67-72, right at the labradorite/bytownite boundary (about 70% anorthite/30% albite).
Evidence grade AScope: An example from Oregon samples; boundary assignment follows the Ab-An-Or ternary diagram.
Ponderosa gave Ab28-32An67-72Or0.3-0.4, Dust Devil Ab28-36An64-72Or0.3-0.8; both plot as labradorite-bytownite on the Ab-An-Or ternary diagram.
Evidence grade AScope: LA-ICP-MS compositional data for specific mines; it does not represent the full bytownite range.
Ethiopian sunstone samples mostly classify as labradorite, with only one spot giving bytownite; oriented needle-like iron oxide inclusions are especially common in calcic plagioclase including bytownite.
Evidence grade AScope: From Ethiopian sample composition data and a general note on inclusion distribution, respectively.
Limits of this research
- Research status: Only partial material-specific findings found; gaps are stated as gaps
- The sources do not define the exact An limits of bytownite; the range used here (about An70-90) is conventional.
- The sources give no absolute age or duration for bytownite phenocryst crystallization itself, only the 15-17 Ma host-basalt age.
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
- Bytownite
GB/T 16552—2017 5.1.1 b) · CIBJO Gemmological Laboratories Book 2024 §7.2.1.35 “Bytownite”
Construction or treatment status
Natural identity; treatment status unknown
Treatments recorded for this material: Filled / Fracture-filled (via parent material), Coated (via parent material), Diffusion-treated (via parent material), Irradiated (via parent material)
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
Bytownite is Bytownite; plagioclase feldspar intermediate variety; use "Bytownite" for listings, and disclose any known treatments.
What this means for you
Before buying, check the recommended listing name "Bytownite" and any disclosed treatments on this page, and ask the seller for a grading report if in doubt.
Known uncertainty
- Last reviewed
- 2026-09-01
Care and wear
No care facts are recorded for this entry itself. Its parent material has care records: see Feldspar.
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 |
|---|---|---|---|---|---|
| Filling | — | — | Graded — see §5.4.1, Table 1 | — | — |
| Coating | — | — | Treatment | — | — |
| Diffusion | — | — | Treatment | — | — |
| Irradiation | — | — | Treatment | — | — |
“—” means the cited source gives no value for that item, not “none”. Source: GB/T 16552—2017 Table B.1 (row for Feldspar)
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
Standard and listing namesBytownite is not listed in Annex A of the GB/T standard and, under the naming rules of GB/T 16552—2017, can be named directly; the suggested listing name is Bytownite, and the mineral or material name is likewise Bytownite. Trade and mineralogical namesThe mineralogical name is Bytownite, an intermediate member of the plagioclase series. Names in four languagesThe four-language names are the Simplified and Traditional Chinese names, English Bytownite and the Japanese names, with the GSJ (Japan) formal name written in kanji. Institution usageFor authority wording, the CIBJO Gemmological Laboratories Book 2024 records Bytownite; the FTC text on file has no wording for this name (checked); GIA and Gem-A are unchecked, and bodies without a recorded wording show the entry's own English name, which does not represent their position.
- GSJ (Japan) formal name
- 亜灰長石
- Mineral / material name (not in GB/T 16552 Annex A; usable directly)
- 倍长石 (GB/T 16552—2017 §5.1.1 b))
- Mineralogical name
- Bytownite; plagioclase feldspar intermediate variety
Four-language names
- 简体中文
- 倍长石
- 繁體中文
- 倍長石
- English
- Bytownite
- 日本語
- バイトウナイト／亜灰長石
See also: Misleading and prohibited trade names · Supplementary name index
Classification
- Origin
- Natural materials
- Material domain
- Natural inorganic gem materials
- Browsing family
- Feldspar materials
- Identity tier
- Mineral / gemstone variety
- Mineral chemical class
- Silicates
- Construction or treatment status
- Natural identity; treatment status unknown
Treatments listed by standards
Bytownite is covered in GB/T 16552—2017 Annex B, Table B.1 by applying the "Feldspar" row, an application made by this site. Under the "Feldspar" row, filling is graded, while coating, diffusion and irradiation are all categorised as treatment. The explanation of Table B.1 and the definitions of the grades are on this site's Gem treatments page, and the full row including the effect column is on the Feldspar page.
GB/T 16552-2017, Annex B, Table B.1
Under the “Feldspar” row of Table B.1: Filling Graded — see §5.4.1, Table 1; Coating Treatment; Diffusion Treatment; Irradiation Treatment. The full row, with the effect column, is on the Feldspar page.
What Table B.1 is, and how the “see 5.4.1” grades are defined: see the GB/T 16552: optimization vs treatment page.
What it is and how it's identified
The composition of Bytownite is registered under plagioclase (the whole series), between NaAlSi3O8 and CaAl2Si2O8. Facts registered under feldspar (the whole mineral group), and not measured on bytownite alone, are: crystalline, with tabular or short prismatic crystals; Mohs hardness 6–6.5, with two sets of perfect cleavage; density 2.55–2.75 g/cm³, refractive index 1.508–1.572 and birefringence 0.005–0.01, the clause also having finer sub-ranges, with the overall value taken; optically anisotropic, biaxial, positive or negative; iridescence, cat's-eye effect, star effect and aventurescence may all be seen; when untreated, pleochroism is usually absent and the lustre is vitreous. Bytownite is transparent to translucent, with a body colour of colourless, yellowish or reddish brown, treatment status untreated; colourless also appears in the colour descriptions of entries such as andesine, cassiterite and danburite in Chapter 7 of the CIBJO Gemmological Laboratories Book. Fluorescence, UV-Vis spectrum, infrared spectrum and magnification are given in the material facts of the feldspar entry.
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 feldspar (the whole mineral group), so they are not repeated on the Bytownite page; see the material facts on the Feldspar entry.
Items below that name the class they cover give the cited clause’s value for that whole class, not a measurement of Bytownite (how to read class-level values).
Definition
Bytownite — composition (chemistry): plagioclase: NaAlSi3O8–CaAl2Si2O8.
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- plagioclase (the whole series)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 Chemical composition · Plagioclase (locator checked 2026-09-28)
- Fact checked on
- 2026-09-26
Structure
Bytownite — structure (overall): crystalline
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Bytownite — structure (crystal system): Moonstone and amazonite belong to the monoclinic or triclinic system; sunstone and labradorite are triclinic.
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Bytownite — structure (crystal habit): Crystals are tabular or stubby prisms; Carlsbad, polysynthetic and gridiron (cross-hatched) twinning are common.
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Durability
Bytownite — Mohs hardness: 6–6.5
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
- feldspar (the whole mineral group)
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Bytownite — cleavage: two directions of perfect cleavage
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Physical properties
Bytownite — density: 2.55–2.75 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
- General note
- the clause has finer ranges
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Optical
Bytownite — optic character: biaxial and anisotropic; optic sign may be either positive or negative.
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Bytownite — refractive index: 1.508–1.572
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
- General note
- the clause has finer ranges
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Bytownite — birefringence: 0.005–0.01
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
- General note
- the clause has finer ranges
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Bytownite — transparency: transparent, translucent.
CIBJO Gemmological Laboratories Book 2024
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Bytownite — pleochroism: usually absent
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Bytownite — optical effect (iridescence): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Bytownite — optical effect (chatoyancy): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Bytownite — optical effect (asterism): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Bytownite — optical effect (aventurescence): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Bytownite — body colour: Colourless, yellowish, reddish brown.
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- untreated
- Qualification
In chapter 7 of the CIBJO Gemmological Laboratories Book, the colour descriptions of Andesine, Cassiterite, Danburite and other entries also name colourless.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
- CIBJO definitions
- chatoyancy, asterism, aventurescence
Quality factors
Bytownite — quality factor (lustre): vitreous
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- feldspar (the whole mineral group)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (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): 1.54 / 2.65; Closest values: 1Charoite 1.554 / 2.66, 2Changhua Stone 1.56 / 2.6, 3Shoushan Stone 1.56 / 2.7, 4Balin Stone 1.56 / 2.55, 5Bamboo Coral 1.57 / 2.65
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 Bytownite under “Feldspar” (§6.1.33): see identification on the Feldspar entry; the required tests are listed on the CIBJO laboratory protocol table for Feldspar.
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
In the clause-level definitions of CIBJO Gemmological Laboratories Book 2024, Bytownite is listed under the entry name Bytownite. The readable definition describes it as a plagioclase feldspar and gives the range of the albite to anorthite molar ratio. The cross-check result is that it is defined directly by CIBJO, and no identically named English entry was found in this edition of the GB/T annex.
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| Term | Clause | Definition | Cross-check |
|---|---|---|---|
| Bytownite | 7.2.1.35 | A plagioclase feldspar with an albite : anorthite molar ratio ranging from 10 : 90 to 30 : 70. Colourless, yellowish, reddish brown, labradorescent; transparent, translucent | Defined directly by CIBJO; no identically named English entry was found in this edition of 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.
- GIA – Gemological Institute of America (United States). Gem Encyclopedia.
- Gem-A – The Gemmological Association of Great Britain (United Kingdom).
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 Feldspar on this site: 13 entries listed by this site's parent-entry links; synthetic, treated and similar entries carry their recorded state after the name; this page (Bytownite) is marked.
This table scrolls sideways on narrow screens.
| Page | Content | Status |
|---|---|---|
| Browsing family | Feldspar materials | Live |
| Treatments recorded for this material | Filled / Fracture-filled (via parent material), Coated (via parent material), Diffusion-treated (via parent material), Irradiated (via parent material) | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Bytownite 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.