Weeksite
A valid IMA mineral species
This page kindly sponsored by Mary Dowse
About Weeksite
Alice M. D. Weeks
Formula:
K2(UO2)2(Si5O13) · 4H2O
Colour:
Yellow
Lustre:
Waxy, Silky
Hardness:
1 - 2
Specific Gravity:
4.1
Crystal System:
Monoclinic
Name:
Named in 1960 by W. F. Osterbridge, Mortimer Hay Staatz, Robert Meyrowitz, and A. M. Plummer in honour of Alice Mary Dowse Weeks (26 August 1909, Sherborn, Massachusetts, USA - 27 August 1988, Bryn Mawr, Pennsylvania, USA), mineralogist for the United States Geological Survey and later professor of mineralogy, Temple University (Philadelphia, USA).
The crystal structure of the mineral is based on a microporous uranyl silicate framework wherein the channels contain (disordered) alkali cation and water sites. Thou the degree of hydration may vary depending on the external conditions, e.g. relative humidity even at room temperature, the silicate framework remains stable upon thermal treatment and ion exchange processes. The exchange capacity is to a certain extent similar to that of zeolites, yet the processes are selective. For instance, Rb+ can be easily substituted by K+ and Cs+, yet no substitution was observed under the same conditions by Na+ or Ag+ even though both K- and Na-based synthetic weeksite analogs have been reported.
Structurally related to barronite.
Structurally related to barronite.
Unique Identifiers
Mindat ID:
4255
Long-form identifier:
mindat:1:1:4255:6
Similar Names
| Wicksite | A valid IMA mineral species | NaCa2(Fe2+,Mn2+)4MgFe3+(PO4)6 · 2H2O |
IMA Classification of Weeksite
Approved
IMA Formula:
K2(U6+O2)2(Si5O13)·4H2O
First published:
1960
Classification of Weeksite
9.AK.30
9 : SILICATES (Germanates)
A : Nesosilicates
K : Uranyl neso- and polysilicates
9 : SILICATES (Germanates)
A : Nesosilicates
K : Uranyl neso- and polysilicates
53.3.2.1
53 : NESOSILICATES Insular SiO4 Groups and Other Anions or Complex Cations
3 : Insular SiO4 Groups and Other Anions of Complex Cations with (UO2)
53 : NESOSILICATES Insular SiO4 Groups and Other Anions or Complex Cations
3 : Insular SiO4 Groups and Other Anions of Complex Cations with (UO2)
14.16.5
14 : Silicates not Containing Aluminum
16 : Silicates of U
14 : Silicates not Containing Aluminum
16 : Silicates of U
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 |
|---|---|---|
| Wks | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Pronunciation of Weeksite
Pronunciation:
| Play | Recorded by | Country |
|---|---|---|
| Jolyon Ralph | United Kingdom |
Physical Properties of Weeksite
Waxy, Silky
Transparency:
Transparent, Translucent
Colour:
Yellow
Hardness:
1 - 2 on Mohs scale
Cleavage:
Distinct/Good
Two good prismatic cleavages noted.
Two good prismatic cleavages noted.
Density:
4.1 g/cm3 (Measured) 3.710 g/cm3 (Calculated)
Optical Data of Weeksite
Type:
Biaxial (-)
RI values:
nα = 1.596 nβ = 1.603 nγ = 1.606
2V:
Measured: 60° , Calculated: 66°
Max. Birefringence:
δ = 0.010
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. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
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. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
Moderate (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Dispersion:
r < v weak
Pleochroism:
Strong
Comments:
X = colorless, Y = pale yellow-green, Z = yellow-green.
Chemistry of Weeksite
Mindat Formula:
K2(UO2)2(Si5O13) · 4H2O
Element Weights:
Common Impurities:
Al,Fe,Ca,Ba,Na,C
Crystallography of Weeksite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/m
Setting:
C2/m
Cell Parameters:
a = 14.2183(8) Å, b = 14.1794(6) Å, c = 9.6229(6) Å
β = 111.445(7)°
β = 111.445(7)°
Ratio:
a:b:c = 1.003 : 1 : 0.679
Unit Cell V:
1,805.73 ų (Calculated from Unit Cell)
Z:
1
Twinning:
By two-fold rotation around [401].
The correct model (reticular twin, diffraction type II; Petříček et al. 2016) involves a two-fold axis operation (or mirror, as an alternative co-set) in (101), which leads to an orthorhombic lattice of four-times larger volume of the unit-cell.
The correct model (reticular twin, diffraction type II; Petříček et al. 2016) involves a two-fold axis operation (or mirror, as an alternative co-set) in (101), which leads to an orthorhombic lattice of four-times larger volume of the unit-cell.
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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Polyhedra Off | Si Polyhedra | All Polyhedra
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View
CIF File Best | x | y | z | a | b | c
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Rotation
Stop | Start
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Labels
Console Off | On | Grey | Yellow
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0018760 | Weeksite | Fejfarova K, Plasil J, Yang H, Cejka J, Dusek M, Downs R T, Barkley M C, Skoda R (2012) Revision of the crystal structure and chemical formula of weeksite, K2(UO2)2(Si5O13)*4H2O American Mineralogist 97 750-754 | 2012 | Anderson mine, Arizona, USA | 0 | 293 | |
| 0000839 | Weeksite | Stohl F V, Smith D K (1981) The crystal chemistry of the uranyl silicate minerals American Mineralogist 66 610-625 |  | 1981 | Anderson mine, Yavapai County, Arizona, USA | 0 | 293 |
| 0005712 | Weeksite | Jackson J M, Burns P C (2001) A re-evaluation of the structure of weeksite, a uranyl silicate framework mineral The Canadian Mineralogist 39 187-195 | | 2001 | 0 | 293 | |
| 0018510 | Weeksite | Baturin S V (1985) Crystal-structure of weeksite Doklady Akademii Nauk SSSR 282 1132-1136 | 1985 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 7.11 Å | (10) |
| 5.57 Å | (9) |
| 8.98 Å | (8) |
| 3.55 Å | (7) |
| 3.30 Å | (7) |
| 2.91 Å | (6) |
| 3.20 Å | (5) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 47a : [Near-surface hydration of prior minerals] | |
| 47f : [Uranyl (U⁶⁺) minerals] |
Geological Setting:
it is formed as a product of the relatively mild hydrothermal transformation of the parental rocks.
Type Occurrence of Weeksite
General Appearance of Type Material:
Yellow radiating fibrous clusters
Place of Conservation of Type Material:
National Museum of Natural History (Smithsonian), Washington, D.C., USA, 128713, 115886, 121949.
Geological Setting of Type Material:
In opal veinlets and as replacements of pebbles in tuffaceous conglomerate.
Associated Minerals at Type Locality:
Other Language Names for Weeksite
Common Associates
Associations Based on Photo Data:
| 18 photos of Weeksite associated with Carnotite | K2(UO2)2(VO4)2 · 3H2O |
| 12 photos of Weeksite associated with 'Chalcedony' | SiO2 |
| 11 photos of Weeksite associated with Autunite | Ca(UO2)2(PO4)2 · 10-12H2O |
| 10 photos of Weeksite associated with Quartz | SiO2 |
| 8 photos of Weeksite associated with Opal | SiO2 · nH2O |
| 6 photos of Weeksite associated with Calcite | CaCO3 |
| 6 photos of Weeksite associated with Goethite | Fe3+O(OH) |
| 6 photos of Weeksite associated with Becquerelite | Ca(UO2)6O4(OH)6 · 8H2O |
| 6 photos of Weeksite associated with Natrozippeite | Na5(UO2)8(SO4)4O5(OH)3 · 12H2O |
| 4 photos of Weeksite associated with Bluelizardite | Na7(UO2)(SO4)4Cl(H2O)2 |
Related Minerals - Strunz-mindat Grouping
| 9.AK. | 'Orlite' | Pb3(UO2)3(Si2O7)2 · 6H2O |
| 9.AK.05 | Soddyite | (UO2)2SiO4 · 2H2O |
| 9.AK.10 | Sklodowskite | Mg(UO2)2(SiO3OH)2 · 6H2O |
| 9.AK.10 | Cuprosklodowskite | Cu(UO2)2(SiO3OH)2 · 6H2O |
| 9.AK.10 | Oursinite | Co(UO2)2(SiO3OH)2 · 6H2O |
| 9.AK.15 | Parauranophane | Ca(UO2)2(SiO3OH)2 · 5H2O |
| 9.AK.15 | Uranophane | Ca(UO2)2(SiO3OH)2 · 5H2O |
| 9.AK.15 | Natroboltwoodite | Na(UO2)(SiO3OH) · H2O |
| 9.AK.15 | Kasolite | Pb(UO2)(SiO4) · H2O |
| 9.AK.15 | Boltwoodite | (K,Na)(UO2)(SiO3OH) · 1.5H2O |
| 9.AK.20 | Swamboite-(Nd) | Nd0.333[(UO2)(SiO3OH)](H2O)~2.5 |
| 9.AK.25 | Haiweeite | Ca(UO2)2[Si5O12(OH)2] · 6H2O |
| 9.AK.25 | Metahaiweeite | Ca(UO2)2Si6O15 · nH2O |
| 9.AK.30 | Coutinhoite | ThxBa(1-2x)(UO2)2Si5O13 · (H2O)1+y (0 < x < 0.5 and 0 < y < (2+x)) |
| 9.AK.30 | Barronite | (◻0.5Ba0.5)(UO2)2Si5O12(OH) · 2H2O |
| 9.AK.35 | Magnioursilite | Mg4(UO2)4(Si2O5)5(OH)6 · 20H2O |
| 9.AK.35 | Calcioursilite | Ca4(UO2)4(Si2O5)5(OH)6 · 15H2O |
| 9.AK.40 | Uranosilite | UO3 · 7SiO2 |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 45.8306% | 11,457,650 | α, β, γ |
| Thorium (Th) | 0.0000% | 0 | α, β, γ |
| Potassium (K) | 7.5281% | 2,334 | 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:
Contains uranium. Always wash hands after handling. Do not lick or ingest. Store in an uninhabited area
Internet Links for Weeksite
mindat.org URL:
https://www.mindat.org/min-4255.html
Please feel free to link to this page.
Please feel free to link to this page.
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External Links:
Mineral Dealers:
References for Weeksite
Reference List:
Outerbridge, W. F., Staatz, M. H., Meyrowitz, R., Pommer, A. M. (1960) Weeksite, a new uranium silicate from the Thomas Range, Juab County, Utah. American Mineralogist, 45 (1-2) 39-52
(1962) International Mineralogical Association: Commission on New Minerals and Mineral Names. Mineralogical Magazine and Journal of the Mineralogical Society, 33 (258) 260-263 doi:10.1180/minmag.1962.033.258.09
Deliens, Michel (1977) Présence de weeksite aux Bois Noirs, massif du Forez (Loire) Bulletin de Minéralogie, 100 (5) 275 doi:10.3406/bulmi.1977.7149
Stohl, Frances V., Smith, Deane K. (1981) The crystal chemistry of the uranyl silicate minerals. American Mineralogist, 66 (5-6) 610-624
Biwer, Bruce M., Ebert, William L., Bates, John K. (1990) The Raman spectra of several uranyl-containing minerals using a microprobe. Journal of Nuclear Materials, 175 (3). 188-193 doi:10.1016/0022-3115(90)90205-2
Jackson, J. M., Burns, P. C. (2001) A re-evaluation of the structure of weeksite, a uranyl silicate framework mineral. The Canadian Mineralogist, 39 (1) 187-195 doi:10.2113/gscanmin.39.1.187
Jambor, John L., Roberts, Andrew C. (2001) New mineral names. American Mineralogist, 86 (9) 1112-1115
Burns, Peter C. (2005) U6+ minerals and inorganic compounds: insights into an expanded structural hierarchy of crystal structures. The Canadian Mineralogist, 43 (6) 1839-1894 doi:10.2113/gscanmin.43.6.1839
Frost, Ray L., Čejka, Jiří, Weier, Matt L., Martens, Wayde, Kloprogge, J. Theo (2006) A Raman and infrared spectroscopic study of the uranyl silicates—Weeksite, soddyite and haiweeite. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 64 (2) 308-315 doi:10.1016/j.saa.2005.07.028
Frost, Ray L., Čejka, Jiří, Weier, Matt L., Martens, Wayde (2006) A Raman and infrared spectroscopic study of the uranyl silicates—Weeksite, soddyite and haiweeite: Part 2. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 63 (2) 305-312 doi:10.1016/j.saa.2005.05.015
Fejfarova, K., Plasil, J., Yang, H., Cejka, J., Dusek, M., Downs, R. T., Barkley, M. C., Skoda, R. (2012) Revision of the crystal structure and chemical formula of weeksite, K2(UO2)2(Si5O13)·4H2O. American Mineralogist, 97 (4) 750-754 doi:10.2138/am.2012.4025
Nazarchuk, Evgeny V.; Siidra, Oleg I.; Tagirova, Yana G.; Charkin, Dmitri O.; Plášil, Jakub; Kasatkin, Anatoly V.; Kalmykov, Stepan N.; Dmitriev, Dmitri N. (2025) Polythermal studies of weeksite, a microporous uranyl silicate, and its synthetic analogues. Mineralogical Magazine, 1-22 doi:10.1180/mgm.2025.10149
Localities for Weeksite
Showing 54 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.
Algeria | |
| MEKTI et al. (2025) |
Australia | |
| Brugger et al. (2003) +1 other reference |
Austria | |
| Brandstätter et al. (1987) +1 other reference |
Brazil | |
| Pires et al. (2014) |
| Bruno Gioia specimen +1 other reference |
| Revista Brasileira de Geociências 24 (1) +1 other reference |
| Fosfatos e Silicatos Secundários de ... | |
Chile | |
| According to Dr. Tony Kampf |
China | |
| Abudukeyumu et al. (2022) |
Czech Republic | |
| Pauliš P. et al. (Kutna Hora, issue 1) |
| Hloušek et al. (2002) |
| Pauliš P. et al. (Kutna Hora, issue 1) |
Egypt | |
| 52 (2) +1 other reference |
France | |
| Favreau (n.d.) |
Germany | |
| Walenta (1989) +1 other reference |
| Lorenz (1998) +1 other reference |
| Witzke (2018) |
Japan | |
| K. Watanabe (1976) |
Mexico | |
| Panczner (1987) |
| Panczner (1987) | |
| Panczner (1987) +4 other references | |
| Panczner (1987) | |
| Panczner (1987) | |
Namibia | |
| von Bezing (2007) |
Peru | |
| O'Connor et al. (2018) |
| Geological Association of Canada (2014) +1 other reference | |
Romania | |
| Hîrtopanu P. et al. (2004) |
USA | |
| Anthony et al. (1995) |
| Anthony et al. (1995) |
| Honea (1959) +2 other references |
| Outerbridge et al. (1960) +2 other references |
| American Mineralogist (1970) |
| Nevada Bureau of Mines and Geology ... +1 other reference |
| NBMG files No. 50600003 +1 other reference | |
| Castor et al. (2004) | |
| - (2005) |
| |
| Castor et al. (2004) | |
| Castor et al. (2004) |
| Northrop et al. (1996) |
| Outerbridge et al. (1960) | |
| Northrop et al. (1996) | |
| AmMin.45:39 +2 other references |
| - (2005) |
| Smith (1991) | |
| Am.Min.: 45: 39-52 |
| King (n.d.) |
| Bullock (1981) |
| SLIDES OF THE FLUORSPAR | |
| Bullock (1981) | |
| Outerbridge et al. (1960) +1 other reference |
| Bullock (1981) | |
| Collection of Alex Earl |
| Outerbridge et al. (1960) |
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