Selwynite
A valid IMA mineral species
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About Selwynite
Alfred Richard Cecil Selwyn
Formula:
NaK(Be,Al)Zr2(PO4)4 · 2H2O
Colour:
Deep purplish blue
Lustre:
Vitreous
Hardness:
4
Specific Gravity:
3.08 (Calculated)
Crystal System:
Tetragonal
Member of:
Name:
The name honours Alfred Richard Cecil Selwyn (1824-1902), British born geologist, founding Director of the Geological Survey of Victoria, Australia (1860-1869), and the second Director of the Geological Survey of Canada (1869-1895).
Gainesite Group
Unique Identifiers
Mindat ID:
7287
Long-form identifier:
mindat:1:1:7287:4
Similar Names
| Celanite | A synonym of 'Ceraltite' | |
| Selenite | A variety of Gypsum | CaSO4 · 2H2O |
| Selenite (of Rau) | A synonym of Berzelianite | |
| Selwynite (of Ulrich) | ||
| Sillénite | A valid IMA mineral species - grandfathered | Bi12SiO20 |
IMA Classification of Selwynite
Approved
IMA Formula:
NaKBeZr4+2(PO4)4·2H2O
Approval year:
1993
Classification of Selwynite
8.CA.20
8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H2O
A : With small and large/medium cations
8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H2O
A : With small and large/medium cations
40.5.4.3
40 : HYDRATED NORMAL PHOSPHATES,ARSENATES AND VANADATES
5 : AXO4·xH2O
40 : HYDRATED NORMAL PHOSPHATES,ARSENATES AND VANADATES
5 : AXO4·xH2O
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Swy | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Selwynite
Vitreous
Transparency:
Transparent, Translucent
Colour:
Deep purplish blue
Comment:
may be pale lavender if weathered.
Streak:
Lavender, pale
Hardness:
4 on Mohs scale
Fracture:
Sub-Conchoidal
Density:
3.08 g/cm3 (Calculated)
Optical Data of Selwynite
Type:
Uniaxial (+)
RI values:
nω = 1.624(2) nε = 1.636(2)
Max. Birefringence:
δ = 0.012
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars.
Surface Relief:
Moderate
Pleochroism:
Visible
Comments:
O = medium bluish lavender; E = very pale bluish lavender.
Chemistry of Selwynite
Mindat Formula:
NaK(Be,Al)Zr2(PO4)4 · 2H2O
Element Weights:
Common Impurities:
Rb,Ca,Sr,Ba,Mg,Mn,Fe,Cs,Ce,Hf,P,Si,F
Crystallography of Selwynite
Crystal System:
Tetragonal
Class (H-M):
4/mmm(4/m2/m2/m) - Ditetragonal Dipyramidal
Space Group:
I41/amd
Setting:
I41/amd
Cell Parameters:
a = 6.570(3) Å, c = 17.142(6) Å
Ratio:
a:c = 1 : 2.609
Unit Cell V:
739.93 ų (Calculated from Unit Cell)
Z:
2
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 6.161 Å | (100) |
| 3.286 Å | (50) |
| 3.039 Å | (30) |
| 4.291 Å | (25) |
| 2.895 Å | (20) |
| 2.609 Å | (5) |
| 2.431 Å | (5) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 22 : Hydration and low-? subsurface aqueous alteration (see also #23) |
Type Occurrence of Selwynite
General Appearance of Type Material:
anhedral, indistinct, in radiating groups
Place of Conservation of Type Material:
Museum Victoria, Melbourne, Australia, M42492, M42590.
Associated Minerals at Type Locality:
Synonyms of Selwynite
Other Language Names for Selwynite
Relationship of Selwynite to other Species
Member of:
Other Members of Gainesite Group:
| Gainesite | Na(Na,K)(Be,Li)Zr2(PO4)4 · 1.5-2H2O | Tet. 4mm : I41md |
| Mccrillisite | NaCs(Be,Li)Zr2(PO4)4 · 1-2H2O | Tet. 4/mmm(4/m2/m2/m) : I41/amd |
Common Associates
Associations Based on Photo Data:
| 2 photos of Selwynite associated with Rockbridgeite | (Fe2+0.5Fe3+0.5)2Fe3+3(PO4)3(OH)5 |
| 2 photos of Selwynite associated with Cyrilovite | NaFe3+3(PO4)2(OH)4 · 2H2O |
| 1 photo of Selwynite associated with Eosphorite | Mn2+Al(PO4)(OH)2 · H2O |
| 1 photo of Selwynite associated with Meurigite-K | KFe3+8(PO4)6(OH)7 · 6.5H2O |
Related Minerals - Strunz-mindat Grouping
| 8.CA. | Apexite | NaMg(PO4) · 9H2O |
| 8.CA. | Brandãoite | BeAl2(PO4)2(OH)2(H2O)5 |
| 8.CA. | Davidlloydite | Zn3(AsO4)2 · 4H2O |
| 8.CA.05 | Parafransoletite | Ca3Be2(PO4)2(PO3OH)2 · 4H2O |
| 8.CA.05 | Fransoletite | Ca3Be2(PO4)2(PO3OH)2 · 4H2O |
| 8.CA.10 | Ehrleite | Ca4Be3Zn2(PO4)6 · 9H2O |
| 8.CA.15 | Faheyite | Be2Mn2+Fe3+2(PO4)4 · 6H2O |
| 8.CA.20 | Mccrillisite | NaCs(Be,Li)Zr2(PO4)4 · 1-2H2O |
| 8.CA.20 | Gainesite | Na(Na,K)(Be,Li)Zr2(PO4)4 · 1.5-2H2O |
| 8.CA.25 | Pahasapaite | Li8(Ca,Li,K)10.5Be24(PO4)24 · 38H2O |
| 8.CA.30 | Nizamoffite | Mn2+Zn2(PO4)2(H2O)4 |
| 8.CA.30 | Arsenohopeite | Zn3(AsO4)2 · 4H2O |
| 8.CA.30 | Hopeite | ZnZn2(PO4)2 · 4H2O |
| 8.CA.35 | Warikahnite | Zn3(AsO4)2 · 2H2O |
| 8.CA.40 | Phosphophyllite | Zn2Fe 2+(PO4)2 · 4H2O |
| 8.CA.42 | Steinmetzite | Zn2Fe3+(PO4)2(OH) · 3H2O |
| 8.CA.45 | Parascholzite | CaZn2(PO4)2 · 2H2O |
| 8.CA.45 | Scholzite | CaZn2(PO4)2 · 2H2O |
| 8.CA.50 | Keyite | Cu2+3Zn4Cd2(AsO4)6 · 2H2O |
| 8.CA.55 | Pushcharovskite | K0.6Cu18[AsO2(OH)2]4[AsO3OH]10(AsO4)(OH)9.6 · 18.6H2O |
| 8.CA.60 | Prosperite | Ca2Zn4(AsO4)4 · H2O |
| 8.CA.65 | Gengenbachite | KFe3+3(PO3OH)4[PO2(OH)2]2 · 6H2O |
| 8.CA.70 | Parahopeite | Zn3(PO4)2 · 4H2O |
| 8.CA.70 | Reaphookhillite | MgZn2(PO4)2 · 4H2O |
| 8.CA.75 | Stergiouite | CaZn2(AsO4)2 · 4H2O |
| 8.CA.80 | Limousinite | BaCa[Be4P4O16] · 6H2O |
| 8.CA.85 | Minjiangite | BaBe2(PO4)2 |
| 8.CA.85 | Wilancookite | (Ba5Li2◻)Ba6Be24P24O96 · 26H2O |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 0.0000% | 0 | α, β, γ |
| Thorium (Th) | 0.0000% | 0 | α, β, γ |
| Potassium (K) | 5.8402% | 1,810 | β, γ |
For comparison:
- Banana: ~15 Bq per fruit
- Granite: 1,000–3,000 Bq/kg
- EU exemption limit: 10,000 Bq/kg
Note: Risk is shown relative to daily recommended maximum exposure to non-background radiation of 1000 µSv/year. Note that natural background radiation averages around 2400 µSv/year so in reality these risks are probably extremely overstated! With infrequent handling and safe storage natural radioactive minerals do not usually pose much risk.
Interactive Simulator:
Note: The mass selector refers to the mass of radioactive mineral present, not the full specimen, also be aware that the matrix may also be radioactive, possibly more radioactive than this mineral!
Activity: –
| Distance | Dose rate | Risk |
|---|---|---|
| 1 cm | ||
| 10 cm | ||
| 1 m |
The external dose rate (D) from a radioactive mineral is estimated by summing the gamma radiation contributions from its Uranium, Thorium, and Potassium content, disregarding daughter-product which may have a significant effect in some cases (eg 'pitchblende'). This involves multiplying the activity (A, in Bq) of each element by its specific gamma ray constant (Γ), which accounts for its unique gamma emissions. The total unshielded dose at 1 cm is then scaled by the square of the distance (r, in cm) and multiplied by a shielding factor (μshield). This calculation provides a 'worst-case' or 'maximum risk' estimate because it assumes the sample is a point source and entirely neglects any self-shielding where radiation is absorbed within the mineral itself, meaning actual doses will typically be lower. The resulting dose rate (D) is expressed in microsieverts per hour (μSv/h).
D = ((AU × ΓU) + (ATh × ΓTh) + (AK × ΓK)) / r2 × μshield
Other Information
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Internet Links for Selwynite
mindat.org URL:
https://www.mindat.org/min-7287.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Selwynite
Localities for Selwynite
Showing 1 localities.
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
Australia (TL) | |
| CM 1995 +1 other reference |
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Wycheproof granite quarry, Wycheproof, Buloke Shire, Victoria, Australia