On this page
UnderstandWhat it is, what people ask, how far this page goes
Natural inorganic gem materials · Mineral group / supergroup · Natural identity; treatment status unknown
Feldspar
The higher-level name for feldspar-group minerals, with no single chemical formula; a specific sample should be identified as orthoclase, plagioclase or microcline. 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 Feldspar 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 FeldsparHow far lab testing can go
- Treatments and enhancements of Feldspar4 registered treatments: status, stability, how common they are and identification leads
- Caring for and wearing FeldsparCleaning, heat, chemicals and light, as the cited sources give them
- Hardness, density and refractive index of FeldsparEach value with its source and check date
- Feldspar 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 FeldsparThe listing name to use; what must be disclosed before sale
- Standard clauses that define FeldsparWhich 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
Feldspar is not a single mineral species but a mineral group of chemically varied but structurally related rock-forming aluminium silicates (tectosilicates), one of the most important rock-forming mineral groups in the crust. It is dominated by potassium feldspar (orthoclase, KAlSi3O8) and the plagioclase series (albite NaAlSi3O8 – anorthite CaAl2Si2O8); the alkali feldspar subgroup varies continuously between albite and orthoclase and includes the monoclinic sanidine and orthoclase and the triclinic anorthoclase, albite and microcline, with variety classification requiring crystal structure (X-ray diffraction) rather than routine gemmology. Feldspars occur widely in igneous rocks (e.g. gem-quality anorthoclase as megacrysts in Cenozoic alkali basalt) and metamorphic rocks; gem varieties include moonstone, sunstone, labradorite and amazonite. Many iridescent feldspars owe their optical effects to submicron intergrowth textures formed by solid-state exsolution; low-quality feldspar can be treated to change colour, improve transparency or durability (e.g. plastic/resin filling for transparency, copper diffusion to create red-green colour), and filled moonstone has been confirmed by infrared spectroscopy.
Scope: Applies to explaining feldspar as a mineral group: its overall make-up, genetic environments and gem varieties; formation conditions and optical-phenomenon mechanisms of specific mineral species are given in the entries for each variety. Statements about treatment refer only to artificial colour alteration/filling and are not natural genesis.
Sources G&G Summer 2024 · G&G Winter 2022
Where it forms
Igneous rocks: feldspar is one of the most important rock-forming minerals; gem-quality anorthoclase occurs as megacrysts in Cenozoic alkali basalt or its weathering products.
Sources G&G Summer 2024
Metamorphic rocks and pegmatites: feldspars are widespread, and slowly cooled potassium feldspars may develop exsolution intergrowths.
Sources G&G Summer 2024
How it forms, step by step
Under igneous or metamorphic conditions, melts or fluids bearing Al, Si, Na, K and Ca crystallize feldspar-group minerals.
Sources G&G Summer 2024 · G&G Winter 2022 · G&G Spring 2013
- Gem-Quality Anorthoclase Feldspar from Southeast Vietnam (Gems & Gemology, Summer 2024, Vol. 60, No. 2)
- Fluorescence Characteristics of Two Copper-Diffused Plagioclase Feldspars: Labradorite and Andesine (Gems & Gemology, Winter 2022, Vol. 58, No. 4)
- Infrared Spectroscopic Study of Filled Moonstone (Gems & Gemology, Spring 2013, Vol. 49, No. 1)
Because group members share related structures with continuously varying compositions, continuous solid-solution series form from albite to anorthite (plagioclase) and between albite and orthoclase (alkali feldspar).
Sources G&G Summer 2024 · G&G Winter 2022 · G&G Spring 2013
- Gem-Quality Anorthoclase Feldspar from Southeast Vietnam (Gems & Gemology, Summer 2024, Vol. 60, No. 2)
- Fluorescence Characteristics of Two Copper-Diffused Plagioclase Feldspars: Labradorite and Andesine (Gems & Gemology, Winter 2022, Vol. 58, No. 4)
- Infrared Spectroscopic Study of Filled Moonstone (Gems & Gemology, Spring 2013, Vol. 49, No. 1)
On slow cooling, alkali feldspar solid solutions may exsolve into lamellar intergrowths (perthite), whose submicron nonperiodic form produces structural colours such as moonstone adularescence.
Sources G&G Summer 2024 · G&G Winter 2022 · G&G Spring 2013
- Gem-Quality Anorthoclase Feldspar from Southeast Vietnam (Gems & Gemology, Summer 2024, Vol. 60, No. 2)
- Fluorescence Characteristics of Two Copper-Diffused Plagioclase Feldspars: Labradorite and Andesine (Gems & Gemology, Winter 2022, Vol. 58, No. 4)
- Infrared Spectroscopic Study of Filled Moonstone (Gems & Gemology, Spring 2013, Vol. 49, No. 1)
Low-quality feldspar may be treated in the market: plastic/resin filling of fissures to improve transparency, or copper diffusion to produce red-green colour imitating natural sunstone.
Sources G&G Summer 2024 · G&G Winter 2022 · G&G Spring 2013
- Gem-Quality Anorthoclase Feldspar from Southeast Vietnam (Gems & Gemology, Summer 2024, Vol. 60, No. 2)
- Fluorescence Characteristics of Two Copper-Diffused Plagioclase Feldspars: Labradorite and Andesine (Gems & Gemology, Winter 2022, Vol. 58, No. 4)
- Infrared Spectroscopic Study of Filled Moonstone (Gems & Gemology, Spring 2013, Vol. 49, No. 1)
Link to appearance
Compositional and structural differences within the group give colours from colourless to yellow, brown, green and blue; alkali feldspars with exsolution lamellae may show moonstone adularescence, while those with iron oxide or copper inclusions show sunstone aventurescence or bodycolour.
Sources G&G Winter 2022 · G&G Summer 2024 · G&G Summer 2025
- Fluorescence Characteristics of Two Copper-Diffused Plagioclase Feldspars: Labradorite and Andesine (Gems & Gemology, Winter 2022, Vol. 58, No. 4)
- Gem-Quality Anorthoclase Feldspar from Southeast Vietnam (Gems & Gemology, Summer 2024, Vol. 60, No. 2)
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures
- Structures Behind the Spectacle: A Review of Optical Effects in Phenomenal Gemstones and Their Underlying Nanotextures (PDF)
Timescale
The sources give no absolute age or duration for feldspar crystallization or its secondary textures (only cooling-rate conditions are described).
Sources G&G Summer 2024 · G&G Winter 2022
Supporting findings
Feldspar-group minerals are widespread; in the Cenozoic alkali basalt of southeast Vietnam, gem-quality anorthoclase occurs as megacrysts enclosed in the host rock and in its weathering products.
Evidence grade AScope: Illustrated by the Vietnam Dong Nai locality; not all feldspar occurrence types are covered.
Causes of colour and optical effects
Many iridescent feldspars owe their optical effects to submicron intergrowth textures from solid-state exsolution; iridescent feldspars fall into labradorite, peristerite and moonstone categories by composition.
Evidence grade AScope: Applies to iridescent feldspars with exsolution textures; those lacking it show no such effect.
Other research findings
Feldspar is a mineral group of rock-forming aluminium tectosilicates whose gem varieties include moonstone (orthoclase), sunstone, labradorite (plagioclase) and amazonite (microcline).
Evidence grade AScope: Group-level definition; separate entries cover each variety’s formation and optical effects.
The feldspar end members are orthoclase (KAlSi3O8), albite (NaAlSi3O8) and anorthite (CaAl2Si2O8); across the alkali feldspar subgroup composition varies continuously between albite and orthoclase, and telling the varieties apart depends on crystal structure as determined by X-ray diffraction rather than on routine gemmological tests.
Evidence grade AScope: Three end-member compositions and subgroup division; proportions vary by sample.
Low-quality feldspar can be treated to enhance colour, durability and clarity: plastic/resin filling of moonstone and amazonite to improve transparency, and copper diffusion to create red-green sunstone/andesine; filled moonstone beads were confirmed by infrared spectroscopy to contain a benzene-structure filler (3053 cm⁻¹ and 3038 cm⁻¹) — a treated material, not a natural origin.
Evidence grade AScope: Explicitly separates treatment from natural origin; the improved colour/clarity of treated material is artificial.
Sources G&G Summer 2024 · G&G Winter 2022 · G&G Spring 2013
- Gem-Quality Anorthoclase Feldspar from Southeast Vietnam (Gems & Gemology, Summer 2024, Vol. 60, No. 2)
- Fluorescence Characteristics of Two Copper-Diffused Plagioclase Feldspars: Labradorite and Andesine (Gems & Gemology, Winter 2022, Vol. 58, No. 4)
- Infrared Spectroscopic Study of Filled Moonstone (Gems & Gemology, Spring 2013, Vol. 49, No. 1)
Limits of this research
- Research status: Formation, occurrence or other material-specific findings found in authoritative sources
- The sources give no absolute age or duration for feldspar-group crystallization, only conditions such as cooling rate.
- Species/variety formation details are dispersed across specialist articles; this is a group-level overview, with deposit-specific T/P data in the individual entries.
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
- Feldspar group (state the specific mineral species)
GB/T 16552—2017 Table A.1 “Feldspar” · CIBJO Gemmological Laboratories Book 2024 §7.2.1.87 “Feldspar”
Construction or treatment status
Natural identity; treatment status unknown
Treatments recorded for this material: Diffusion-treated, Filled / Fracture-filled, Coated, Irradiated
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
Feldspar is often subjected to diffusion. Under GB/T 16552-2017, diffusion counts as a treatment and must be stated in the name (§5.4.2.2 a). Do not assume it is unenhanced.
Evidence
- GB/T · Table A.1, row 长石 (Feldspar)
What this means for you
Before buying, check the recommended listing name "Feldspar group (state the specific mineral species)" 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
- Feldspar group (state the specific mineral species)
Care and wear
Care
Feldspar — care (cleaning): Never put it in an ultrasonic cleaner; the best way is a clean cloth dampened with water only, with no soap or other cleaning agent.
CIBJO Retailers' Reference Guide (2021)
- Treatment state
- any treatment state
Source & check 2026-09-26
- Source
- CIBJO Retailers' Reference Guide — Gemstones (November 2021) (CIBJO): p.22, Feldspar group chapter, “Cutting, care and cleaning” (locator checked 2026-09-28)
- Fact checked on
- 2026-09-26
Feldspar — care (setting): With perfect cleavage it is somewhat delicate, so take care in setting; it is often cut as cabochons, which abrade less than faceted stones.
CIBJO Retailers' Reference Guide (2021)
- Treatment state
- any treatment state
Source & check 2026-09-26
- Source
- CIBJO Retailers' Reference Guide — Gemstones (November 2021) (CIBJO): p.22, Feldspar group chapter, “Cutting, care and cleaning” (locator checked 2026-09-28)
- 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
CleaningCan Feldspar be cleaned ultrasonically? The “Cutting, care and cleaning” passage of the feldspar group chapter in the CIBJO Retailer's Reference Guide — Gemstones (November 2021) states that Feldspar should never be put in an ultrasonic cleaner; the best way is to wipe it with a clean cloth dampened with water only, without soap or other cleaning agents. Wear and settingOn wear and setting, the same source states that Feldspar has perfect cleavage and is somewhat delicate, so care is needed when setting it; Feldspar is often cut as cabochons, which are less prone to wear than faceted stones. Both care conclusions apply whatever the treatment state.
This table scrolls sideways on narrow screens.
| Question | Matching entries |
|---|---|
| Can it go in an ultrasonic or steam cleaner? | Never put it in an ultrasonic cleaner; the best way is a clean cloth dampened with water only, with no soap or other cleaning agent |
| Wearing limits (knocks, settings) | With perfect cleavage it is somewhat delicate, so take care in setting; it is often cut as cabochons, which abrade less than faceted stones |
Treatments and identification leads
Registered treatmentsThe registered treatments for Feldspar are coating, diffusion, irradiation and filling. Values not givenCoating, diffusion and filling have the status treated, and irradiation the status irradiated or dyed; stability and prevalence are not given by the cited source, which is not the same as “none”. Leads for coating: abnormal lustre under a loupe, the coating peeling off in places, possibly abnormal refractive index readings, and characteristic peaks of the coating in infrared and Raman spectra. For diffusion, uneven colour distribution is visible under magnification, and composition analysers (for example LIBS) detect abnormal levels of the diffused element (for example copper) in the surface layer. Irradiation turns white microcline into blue amazonite; it is very rare and hard to detect. Filled areas differ in lustre from the host and may show gas bubbles, infrared spectroscopy detects characteristic bands of the filler, and luminescence imaging equipment such as a UV fluorescence viewer can show how the filler is distributed.
This table scrolls sideways on narrow screens.
| Treatment | Market frequency (CIBJO) | Stability (CIBJO) | GB/T 16552 category | JJA/AGL listing | Identification leads |
|---|---|---|---|---|---|
| coatingStatus: treated | — | — | Treatment | — | See identification leads |
| diffusion treatmentStatus: treated | — | — | Treatment | — | See identification leads |
| irradiationStatus: irradiated or dyed | — | — | Treatment | — | See identification leads |
| fillingStatus: treated | — | — | Graded — see §5.4.1, Table 1 | — | See identification leads |
Where each treatment acts (schematics): Coated · Diffusion-treated · Irradiated · Filled / Fracture-filled
“—” means the cited source gives no value for that item, not “none”. Source: GB/T 16553—2017; GB/T 16552—2017 Table B.1
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
The name register below lists one name for Feldspar in a non-Latin script: 1 with no restriction recorded on use as a name.
Standard and listing namesThe GB/T 16552—2017 formal name of Feldspar is given in Table A.1, the mineralogical name is Feldspar-group minerals, and the suggested listing name is Feldspar group (state the specific mineral species). Names in four languagesThe four-language names are the Simplified and Traditional Chinese names, English Feldspar and the Japanese names. Feldspar carries its own Japanese names, and the GSJ (Japan) wording for them is not yet verified. Institution usageFor authority wording, the CIBJO Gemmological Laboratories Book 2024 records Feldspar; the FTC text on file has no wording for Feldspar (checked); GIA and Gem-A are unchecked. Bodies without a recorded wording show the entry's own English name for Feldspar, which does not represent their position. Candidate search termsAccording to the JJA/AGL Gemstone Nomenclature 2025 p.15, a Japanese transliteration is a search candidate only, with no restriction recorded on its use as a name.
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) | ||||
| フェルスパーJapanese | transliteration | search candidate only | no restriction recorded | JJA/AGL Gemstone Nomenclature 2025 p.15 |
How each authority words this name: see Names › Authority wording.
- GSJ (Japan) formal name
- 長石／フェルドスパー (not yet checked for this body — the entry's own Japanese name is shown)
- Chinese formal name
- 长石 (GB/T 16552—2017 Table A.1)
- Mineralogical name
- Feldspar-group minerals
Four-language names
- 简体中文
- 长石
- 繁體中文
- 長石
- English
- Feldspar
- 日本語
- 長石／フェルドスパー
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 group / supergroup
- Mineral chemical class
- Silicates
- Construction or treatment status
- Natural identity; treatment status unknown
Treatments listed by standards
For Feldspar, the Feldspar row of GB/T 16552—2017, Annex B, Table B.1 lists these methods: filling, which improves or changes durability and appearance, graded; coating, which improves or changes lustre, colour and other aspects of appearance, classed as treatment; diffusion, which improves or changes colour, classed as treatment; and irradiation, which changes colour, classed as treatment. What Table B.1 is and how the filling grades are defined are explained on this site's Gem treatments page.
GB/T 16552-2017, Annex B, Table B.1
Table B.1, row “Feldspar” (p.15):
This table scrolls sideways on narrow screens.
| Method | Effect | Category |
|---|---|---|
| Filling | Improves or changes durability and appearance | Graded — see §5.4.1, Table 1 |
| Coating | Improves or changes lustre, colour and other aspects of appearance | Treatment |
| Diffusion | Improves or changes colour | Treatment |
| Irradiation | Changes colour | Treatment |
What Table B.1 is, and how the “see 5.4.1” grades are defined: see the GB/T 16552: optimization vs treatment page.
What it is and how it's identified
Registered material facts for Feldspar: the general chemical formula is XAlSi3O8, where X can be Na, K or Ca-Al; potassium feldspar is KAlSi3O8, possibly with Ba, Na, Rb, Sr and other elements, and plagioclase lies between NaAlSi3O8 and CaAl2Si2O8; CIBJO registers the phase as the feldspar group. Structurally, Feldspar is crystalline. Mohs hardness 6–6.5, two directions of perfect cleavage; the site note explains that hardness alone is not enough to judge durability. Density 2.55–2.75 g/cm³, refractive index 1.508–1.572, birefringence 0.005–0.01; the site note explains that the density, refractive index and birefringence clauses have finer sub-ranges and the overall values are registered. Optical character anisotropic, biaxial, positive or negative; iridescence, the cat's-eye effect, asterism and aventurescence can occur. Untreated, Feldspar usually has no pleochroism, its lustre is vitreous, and common body colours range from colourless to light yellow as well as green, orange, brown and others; on body colour, the site note explains that the colour descriptions in the clauses for hemimorphite, garnet, zircon and other varieties in chapter 5 of GB/T 16553—2017 also mention colourless.
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”.
Definition
Feldspar — composition (chemistry): general formula XAlSi3O8, where X stands for Na, K or Ca-Al. Potassium feldspar is KAlSi3O8 and may carry elements such as Ba, Na, Rb and Sr. Plagioclase has a composition lying between NaAlSi3O8 and CaAl2Si2O8.
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-22
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-22)
- Fact checked on
- 2026-09-22
Feldspar — composition (phase): feldspar group
CIBJO Gemmological Laboratories Book 2024
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Structure
Feldspar — structure (overall): crystalline
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — 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
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
Feldspar — 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
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
Durability
Feldspar — 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
- General note
- hardness only, not durability
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
Feldspar — cleavage: two directions of perfect cleavage
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Physical properties
Feldspar — density: 2.55–2.75 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- 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
Feldspar — 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
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
Feldspar — refractive index: 1.508–1.572
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- 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
Feldspar — birefringence: 0.005–0.01
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- 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
Feldspar — pleochroism: usually absent
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — fluorescence (overall): none to weak, white, violet, red, yellow.
GB/T 16553—2017
UV fluorescencewhitevioletredyellownone–weakDots are illustrative colours built from the colour names, not measured values
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — spectrum (UV-visible): generally non-characteristic
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — spectrum (infrared): Feldspar's own diagnostic bands are seen in the mid-IR
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — optical effect (iridescence): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — optical effect (chatoyancy): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — optical effect (asterism): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — optical effect (aventurescence): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — magnification: cleavage, twin striations, gas-liquid inclusions, mineral inclusions, needle-like inclusions and the like; moonstone: visible centipede-like inclusion, visible fingerprint-like inclusions, visible needle inclusions; amazonite: commonly seen grid color spot; sunstone: commonly seen platy inclusions, red or golden, with a metallic look; labradorite: commonly seen twin striations.
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — body colour: usually colourless or pale yellow, though green, orange, brown and similar hues also occur.
By variety — moonstone runs from colourless to white, and its moonlight sheen may look blue, yellow or colourless; amazonite ranges from vivid green and vivid blue-green to pale blue, often mottled in a green-and-white grid; sunstone goes from yellow and orange-yellow to brown and shows a red or golden aventurescent glitter; labradorite may be grey to greyish yellow, orange to brown, brownish red, green or similar, and can show iridescence.
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 Hemimorphite, Garnet, Zircon and other variety clauses also name colourless.
- General note
- colour alone is not identity
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
- CIBJO definitions
- chatoyancy, asterism, aventurescence
Quality factors
Feldspar — quality factor (lustre): vitreous
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
This material (RI / SG midpoints): 1.54 / 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
When Feldspar is coated, a loupe shows abnormal lustre and locally peeling coating layers, the refractive index may be abnormal, and infrared and Raman spectra show characteristic peaks of the coating. In diffusion-treated feldspar, magnification shows uneven colour, and chemical analysis such as LIBS shows abnormal levels of diffused elements (such as copper) in the surface layer. In irradiated feldspar, white microcline can be turned into blue amazonite; this is very rare and hard to detect. In filled feldspar, the filled areas have a lustre different from the stone itself, with visible gas bubbles; the infrared spectrum detects bands of the filler, and luminescence imaging equipment such as a UV fluorescence viewer can show the distribution of the filler. The leads for coating, diffusion, irradiation and filling come from GB/T 16553—2017, which serves only as a reference for feldspar and does not govern it directly. CIBJO's laboratory rules call for particular checks for heating and copper diffusion, for labradorite and andesine only; for orthoclase moonstone, microcline, albite, oligoclase and bytownite they note cat's-eye effect, adularescence and aventurescence, with LA-ICP-MS or SEM-EDS chemical analysis used when varieties need to be distinguished; for labradorite and andesine they note labradorescence and aventurescence.
The tests the CIBJO laboratory protocol requires for this material, and what each method means, are in the protocol table on the laboratory testing page: §6.1.33, §6.1.34.
How far testing can go
Feldspar that has undergone coating can be identified by the following features: Under magnification the surface luster is abnormal and the film can be seen peeling off in places; refractive index readings may be abnormal; infrared and Raman spectra show characteristic peaks of the film.
GB/T 16553—2017
- Treatment state
- treated
- Does this standard apply
- can be followed as a reference only
- Treatment
- coating
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (coating) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar that has undergone diffusion treatment can be identified by the following features: Under magnification the colour is unevenly distributed; compositional analysis (such as LIBS) finds an abnormal amount of a diffused element such as copper in the surface layer.
GB/T 16553—2017
- Treatment state
- treated
- Does this standard apply
- can be followed as a reference only
- Treatment
- diffusion treatment
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (diffusion treatment) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar that has undergone irradiation can be identified by the following features: Treatment can turn white microcline into blue amazonite; this is rarely seen and not easy to detect.
GB/T 16553—2017
- Treatment state
- irradiated or dyed
- Does this standard apply
- can be followed as a reference only
- Treatment
- irradiation
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (irradiation) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar that has undergone filling can be identified by the following features: Under magnification the surface luster of the filled part differs from that of the host stone and gas bubbles are visible in the filled area; infrared spectra show characteristic absorption bands of the filler; luminescence imaging (such as a UV fluorescence viewer) shows how the filler is distributed.
GB/T 16553—2017
- Treatment state
- treated
- Does this standard apply
- can be followed as a reference only
- Treatment
- filling
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.1.17 (filling) (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Feldspar — what the CIBJO laboratory protocol says to watch for: heat, Cu-diffusion
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- any treatment state
- Applies only to
- labradorite and andesine
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Feldspar — notes on test methods in the CIBJO laboratory protocol:
| Test method | What the protocol notes for it |
|---|---|
| Phenomena: | Cat’s-eye, adularescence, aventurescence; |
| LA-ICP-MS or SEM-EDS chemistry: | If needed for variety separation |
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- any treatment state
- Applies only to
- orthoclase moonstone, microcline, albite, oligoclase and bytownite
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Feldspar — notes on test methods in the CIBJO laboratory protocol:
| Test method | What the protocol notes for it |
|---|---|
| Phenomena: | Labradorescence, aventurescence |
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- any treatment state
- Applies only to
- labradorite and andesine
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
Clause-level definitions
Feldspar is defined directly in CIBJO Gemmological Laboratories Book 2024 under the term Feldspar; the definition classes feldspar as a mineral group and states that the CIBJO wording is quoted in full under Clause-level definitions on this page. The cross-check shows it is defined directly by CIBJO and also appears in the GB/T annex.
This table scrolls sideways on narrow screens.
| Term | Clause | Definition | Cross-check |
|---|---|---|---|
| Feldspar | 7.2.1.87 | see albite, amazonite, andesine, anorthite, bytownite, labradorite, microcline, moonstone, rainbow moonstone, oligoclase, orthoclase, spectrolite, sunstone | 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.
- 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.
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 (Feldspar) is marked.
- Feldspar
This table scrolls sideways on narrow screens.
| Page | Content | Status |
|---|---|---|
| Browsing family | Feldspar materials | Live |
| Treatments recorded for this material | Diffusion-treated, Filled / Fracture-filled, Coated, Irradiated | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Feldspar 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.