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UnderstandWhat it is, what people ask, how far this page goes
Natural inorganic gem materials · Mineral species · Natural identity; treatment status unknown
Prehnite
A silicate mineral species used under its standard mineralogical name, Prehnite; the species of any given specimen still needs to be identified. 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 Prehnite 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 PrehniteHow far lab testing can go and whether a synthetic exists
- Caring for and wearing PrehniteCleaning, heat, chemicals and light, as the cited sources give them; durability indicators and wearing advice
- Hardness, density and refractive index of PrehniteEach value with its source and check date
- Prehnite 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?
- Name origin and history of PrehniteWhere the name comes from
- Listing and disclosing PrehniteThe listing name to use
- Standard clauses that define PrehniteWhich 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
Numbers in curly braces, such as {111}, are crystallographic face symbols (Miller indices): each marks a set of crystal faces or cleavage planes. They are reproduced as written in the cited source.
Prehnite is a distinct hydrous calcium-aluminium silicate species, Ca2Al2Si3O10(OH)2, crystallising in the orthorhombic system. It most often appears as a hydrothermal or secondary vein- and cavity-filling (vesicle) mineral in mafic volcanic rocks, more rarely in granite gneiss or syenite, and it characteristically results from low-grade metamorphism. Aggregates are typically fan-shaped, reniform, globular or stalactitic and may be compact and massive; minerals found alongside it include zeolites, datolite, pectolite, calcite, epidote and copper. Its colour runs from light to dark green through white, yellow, grey and pink, and the mineral is colourless in thin section.
Scope: Covers the occurrence, composition and crystal habit of prehnite as a distinct mineral species; not to be used for origin or treatment assessments of specific samples.
Sources Handbook of Mineralogy · CIBJO Gemstone Book 2022
Where it forms
Veins and cavities (vesicles) in mafic (basaltic) volcanic rocks, as a secondary/hydrothermal mineral.
Sources Handbook of Mineralogy
Sometimes found in granite gneiss or syenite; typically generated by low-grade metamorphism.
Sources Handbook of Mineralogy
Common associates: zeolite-group minerals, datolite, pectolite, calcite, epidote and copper.
Sources Handbook of Mineralogy
How it forms, step by step
In veins, vesicles or a metamorphic setting, low-temperature Ca-Al-Si-bearing fluids crystallise to form prehnite.
Sources Handbook of Mineralogy
Low-temperature hydrothermal or low-grade metamorphic conditions control its mode of occurrence (veins, vesicle fillings, metamorphic).
Sources Handbook of Mineralogy
Crystallisation produces fan-like, reniform, globular or stalactitic aggregates, or compact massive material.
Sources Handbook of Mineralogy
In vugs it may develop tabular or prismatic to steep-pyramidal crystals up to 4.5 cm.
Sources Handbook of Mineralogy
Link to appearance
Colour ranges from light to dark green as well as white, yellow, grey and pink, colourless in thin section; the aggregate habit (fan-like, reniform, globular, stalactitic) determines its massive appearance and lustre (vitreous, weakly pearly on {001}).
Sources Handbook of Mineralogy
Timescale
The cited source gives no absolute timescale for prehnite formation.
Sources Handbook of Mineralogy
Supporting findings
Prehnite is found most often as a vein- and cavity-filling mineral of hydrothermal or secondary origin in mafic volcanic rocks, and it characteristically results from low-grade metamorphism.
Evidence grade BScope: Mode of occurrence and formation mechanism; does not name specific localities.
Sources Handbook of Mineralogy
Prehnite is less commonly found in granite gneiss or syenite, and its associated minerals include zeolites, datolite, pectolite, calcite, epidote and copper.
Evidence grade BScope: Host-rock and association description; not uniform across all localities.
Sources Handbook of Mineralogy
Recorded localities
Authoritative sources list the localities below; the list is not exhaustive.
Africa
- Copper Valley, Brandberg, Namibia
Sources Handbook of Mineralogy
- Cape of Good Hope area, South Africa
Sources Handbook of Mineralogy
Europe
- Bourg-d’Oisans, Isère, France
Sources Handbook of Mineralogy
Oceania
- New South Wales, Australia
Sources Handbook of Mineralogy
Seas and coasts
- Worldwide
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
Prehnite's colour ranges light to dark green, white, yellow, grey and pink, colourless in thin section; the source gives no chromophore mechanism.
Evidence grade BScope: Records only the colour range given by the source; the chromophore (e.g. iron) has no authoritative statement in the cited sources.
Sources Handbook of Mineralogy
Where the name comes from
The mineral prehnite commemorates Colonel Hendrik von Prehn (1733–1785), its discoverer.
Evidence grade BScope: This states only the origin of the name and does not establish the material's composition, locality, natural origin, or whether it was treated.
Sources Handbook of Mineralogy
Other research findings
Prehnite, Ca2Al2Si3O10(OH)2, is an independent hydrous calcium-aluminium silicate mineral species.
Evidence grade BScope: Species level; specimens still require identification.
Sources Handbook of Mineralogy
CIBJO's material table lists Prehnite as a gem material with no treatment (always).
Evidence grade AScope: Treatment/nomenclature level; does not guarantee an individual specimen is untreated.
Sources CIBJO Gemstone Book 2022
Prehnite is named after its discoverer, Colonel Hendrik von Prehn.
Evidence grade BScope: Naming origin; not a formation or identification conclusion.
Sources Handbook of Mineralogy
Limits of this research
- Research status: Formation, occurrence or other material-specific findings found in authoritative sources
- The cited source gives no absolute timescale for prehnite formation.
- The source gives no chromophore mechanism for prehnite's colour; it lists only the colour range.
- No locality- or treatment-specific judgement is offered.
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
- Prehnite
GB/T 16552—2017 Table A.2 “Prehnite” · CIBJO Gemmological Laboratories Book 2024 §7.2.1.184 “Prehnite”
Construction or treatment status
Natural identity; treatment status unknown
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
Prehnite is Prehnite; use "Prehnite" for listings, and disclose any known treatments.
What this means for you
Before buying, check the recommended listing name "Prehnite" and any disclosed treatments on this page, and ask the seller for a grading report if in doubt.
- Last reviewed
- 2026-09-01
Care and wear
Care
Prehnite — care (heat): A peer-reviewed 2022 RSC Advances study found that heating yellow-green prehnite in air from 200 to 800 °C progressively reduced its transparency and deepened the yellow; at 800 °C it turned brownish and partly decomposed (laboratory temperatures).
RSC Advances (Wang et al., 2022)
- Treatment state
- any treatment state
Source & check 2026-10-06
- Source
- Q. Wang, Q. Guo, L. Liao, L. Cui & N. Li, “Study of the mechanism of color change of prehnite after heat treatment”, RSC Advances 12(5): 3044–3054 (2022), doi:10.1039/d2ra00318j: Section: main text (locator checked 2026-10-06)
- Fact checked on
- 2026-10-06
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
Each question links to the matching entries on this page; whether they answer it fully, go by the entry wording.
This table scrolls sideways on narrow screens.
Durability and wearing
Toughness
Brittle
VerifyNames, standards, technical facts, clauses and sources
Names
Standard and listing namesThe Chinese formal name of Prehnite in Table A.2 of GB/T 16552—2017 corresponds to Prehnite, and the suggested listing name is Prehnite; the mineralogical name and English name are both Prehnite. Japanese namesThe GSJ (Japan) formal name is the same Chinese-character name. Names in four languagesNames are given in Simplified Chinese, Traditional Chinese, English (Prehnite) and Japanese. Institution usageOn authority wording, the CIBJO Gemmological Laboratories Book 2024 records Prehnite; there is no wording for this name in the FTC text on file, as checked by this site; the wording of GIA and Gem-A is unchecked. Bodies without a recorded wording show the entry's own English name, which does not represent the position of GIA, FTC or Gem-A.
- GSJ (Japan) formal name
- 葡萄石
- Chinese formal name
- 葡萄石 (GB/T 16552—2017 Table A.2)
- Mineralogical name
- Prehnite
Four-language names
- 简体中文
- 葡萄石
- 繁體中文
- 葡萄石
- English
- Prehnite
- 日本語
- プレナイト／葡萄石
See also: Misleading and prohibited trade names · Supplementary name index
Classification
- Origin
- Natural materials
- Material domain
- Natural inorganic gem materials
- Browsing family
- Other silicate minerals
- Identity tier
- Mineral species
- Mineral chemical class
- Silicates
- Construction or treatment status
- Natural identity; treatment status unknown
What it is and how it's identified
Material facts for Prehnite: composition Ca2Al(AlSi3O10)(OH)2, which may contain elements such as Fe, Mg, Mn, Na and K; crystalline or a crystalline aggregate, orthorhombic; Mohs hardness 6–6.5, with one set of cleavage, perfect to moderate, generally not visible in aggregates; density 2.8–2.95 g/cm³. Optically it is anisotropic, biaxial and positive, often an anisotropic aggregate; birefringence is 0.02–0.035, the clause also having finer sub-ranges, with the overall value taken; the refractive index is 1.585–1.665, this site noting that the cited clause gives 1.616–1.649 with an allowed deviation of +0.016/−0.031, from which the registered limits are derived, the clause also having finer sub-ranges, with the overall value taken. When untreated, the quality factor is a vitreous lustre. For body colour, when untreated, GB/T 16553—2017 registers white, light yellow, flesh red and green of various tones, while the CIBJO Blue Book registers it as usually greenish yellow to yellowish green; CIBJO also registers the transparency as translucent.
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
Prehnite — nomenclature status: IMA status G: grandfathered (described before the IMA existed, and generally regarded as a valid species).
CIBJO Gemmological Laboratories Book 2024
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Prehnite — composition (chemistry): Ca2Al (AlSi3O10) (OH) 2, elements such as Fe,Mg,Mn,Na and K may be contained.
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — composition (phase): prehnite
CIBJO Gemmological Laboratories Book 2024
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Structure
Prehnite — structure (overall): crystalline, or else a crystalline aggregate
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — structure (crystal system): orthorhombic system
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — structure (crystal habit): Columnar and platy forms are rare; generally platy, flaky, botryoidal, reniform, radiating or dense massive aggregate.
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Durability
Prehnite — 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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — cleavage: one direction of cleavage, perfect to medium; usually not seen in aggregates.
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Physical properties
Prehnite — density: 2.8–2.95 g/cm³
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Optical
Prehnite — optic character: biaxial, optically positive (anisotropic); usually an anisotropic aggregate.
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — refractive index: 1.585–1.665
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- Qualification
The clause we cite gives 1.616–1.649, with a stated tolerance of +0.016 / -0.031. The range shown here is worked out from that.
- General note
- the clause has finer ranges
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — birefringence: 0.02–0.035
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — transparency: translucent.
CIBJO Gemmological Laboratories Book 2024
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Prehnite — pleochroism: not measurable on an aggregate
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — fluorescence (overall): none
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — spectrum (UV-visible): 438 nm weak absorption band
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — spectrum (infrared): In the mid-IR, prehnite shows its own diagnostic bands.
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — optical effect (chatoyancy): seen; seldom encountered
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Prehnite — magnification: mineral inclusions, fibre-like texture, radiate structure
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): §5.2.17 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
body colour2 sources compared
Prehnite — body colour: white, light yellow, flesh-red, or green with various tints.
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 Amber, Brucite, Balin Stone and other variety clauses also name white or a whitish colour.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.17 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Prehnite — body colour: usually greenish yellow to yellowish green.
CIBJO Gemmological Laboratories Book 2024
- Treatment state
- untreated
- Qualification
In chapter 7 of the CIBJO Gemmological Laboratories Book, the colour descriptions of Chrysoprase, Demantoid, Green Quartz and other entries also name yellow or a yellowish colour.
- General note
- colour alone is not identity
Source & check 2026-09-26
- Source
- Fact checked on
- 2026-09-26
How the sources relate
- GB/T 16553—2017 and CIBJO Gemmological Laboratories Book 2024
Both describe the yellow-green range (GB/T 16553—2017 gives light yellow and green with other tints; the CIBJO Gemmological Laboratories Book gives usually greenish yellow to yellowish green). GB/T 16553—2017 also lists white and pinkish red.
- CIBJO definitions
- chatoyancy
Quality factors
Prehnite — 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): §5.2.17 (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): 1.625 / 2.88; Closest values: 1Achroite 1.635 / 2.86, 2Larimar 1.62 / 2.82, 3Brazilianite 1.611 / 2.97, 4Chlorite 1.629 / 3, 5Bi Yu, Green Nephrite Variety 1.621 / 3
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 tests the CIBJO laboratory protocol requires for Prehnite, and what each method means, are in the protocol table on the laboratory testing page. The CIBJO Blue Book Official Gemstone Book (2022) records that no synthetic counterpart of Prehnite is available on the market.
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: §6.1.63.
How far testing can go
Prehnite — synthetic counterpart on the market: No synthetic counterpart of this material is commercially available
CIBJO Gemstone Book 2022
- Treatment state
- any treatment state
Source & check 2026-09-22
- Source
- Fact checked on
- 2026-09-22
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
Clause-level definitions
Prehnite has a clause-level definition in CIBJO Gemmological Laboratories Book 2024 under the entry name Prehnite, describing it as usually greenish yellow to yellowish green, translucent, and able to show the cat's-eye effect; the cross-check result is that it is defined directly by CIBJO and also appears in the GB/T annex. The IMA Mineral List entry likewise registers the name Prehnite, with the chemical formula Ca2Al(Si3Al)O10(OH)2; the entry is cross-checked against the RRUFF/IMA master mineral list and uses public domain data.
This table scrolls sideways on narrow screens.
| Term | Clause | Definition | Cross-check |
|---|---|---|---|
| Prehnite | 7.2.1.184 | usually greenish yellow to yellowish green, translucent. May show chatoyancy | Defined directly by CIBJO; also present in the GB/T annex. |
| Prehnite | IMA Mineral List entry | Prehnite Ca2Al(Si3Al)O10(OH)2 G 1788 | Cross-checked against the RRUFF/IMA master mineral list (public domain data). |
Evidence and sources
Authority basis and clause sources
Sources
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.
This table scrolls sideways on narrow screens.
| Page | Content | Status |
|---|---|---|
| Browsing family | Other silicate minerals | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Prehnite 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.