Demesmaekerite
A valid IMA mineral species
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About Demesmaekerite
Gaston Demesmaeker (°1911 - 1997)
Formula:
Pb2Cu5(UO2)2(SeO3)6(OH)6 · 2H2O
Colour:
Bottle-green when fresh, turning somewhat brownish on dehydration
Hardness:
3 - 4
Specific Gravity:
5.28
Crystal System:
Triclinic
Name:
Named in 1965 by Fabian Cesbron, B. Bachet, and Robert Oosterbosch in honour of Gaston Demesmaeker [5 March 1911, Halle, Belgium – 13 February 1997, Anderlecht, Belgium], Belgian geologist, former director of the Union Minière du Haut Katanga (UMHK).
Type Locality:
This page provides mineralogical data about Demesmaekerite.
Unique Identifiers
Mindat ID:
1259
Long-form identifier:
mindat:1:1:1259:7
IMA Classification of Demesmaekerite
Approved
IMA Formula:
Pb2+2Cu2+5(U6+O2)2(Se4+O3)6(OH)6·2H2O
Approval year:
1965
First published:
1965
Classification of Demesmaekerite
4.JJ.20
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
J : Arsenites, antimonites, bismuthites, sulfites, selenites, tellurites; iodates
J : Selenites with additional anions, with H2O
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
J : Arsenites, antimonites, bismuthites, sulfites, selenites, tellurites; iodates
J : Selenites with additional anions, with H2O
34.7.6.1
34 : SELENITES, TELLURITES AND SULFITES
7 : Hydrated Selenites, Tellurites and Sulfites containing Hydroxyl or Halogen
34 : SELENITES, TELLURITES AND SULFITES
7 : Hydrated Selenites, Tellurites and Sulfites containing Hydroxyl or Halogen
28.1.10
28 : Selenites, Selenates, Tellurites, and Tellurates
1 : Selenites
28 : Selenites, Selenates, Tellurites, and Tellurates
1 : Selenites
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 |
|---|---|---|
| Dmm | 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 Demesmaekerite
Transparency:
Translucent, Opaque
Colour:
Bottle-green when fresh, turning somewhat brownish on dehydration
Hardness:
3 - 4 on Mohs scale
Cleavage:
None Observed
Density:
5.28(4) g/cm3 (Measured) 5.45 g/cm3 (Calculated)
Optical Data of Demesmaekerite
Type:
Biaxial (+)
RI values:
nα = 1.835 nγ = 1.910
Max. Birefringence:
δ = 0.075
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:
Very High (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.
No measured or calculated 2V is on file for this mineral, so the value used here (92°) is estimated from its recorded refractive indices and optic sign, not from a direct 2V measurement.
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.
No measured or calculated 2V is on file for this mineral, so the value used here (92°) is estimated from its recorded refractive indices and optic sign, not from a direct 2V measurement.
Dispersion:
strong
Pleochroism:
Visible
Comments:
X' = yellow-green; Y' = brown.
Chemistry of Demesmaekerite
Mindat Formula:
Pb2Cu5(UO2)2(SeO3)6(OH)6 · 2H2O
Element Weights:
Crystallography of Demesmaekerite
Crystal System:
Triclinic
Class (H-M):
1 - Pinacoidal
Space Group:
P1
Cell Parameters:
a = 11.94 Å, b = 10.02 Å, c = 5.62 Å
α = 90°, β = 100°, γ = 91.91°
α = 90°, β = 100°, γ = 91.91°
Ratio:
a:b:c = 1.192 : 1 : 0.561
Unit Cell V:
661.78 ų (Calculated from Unit Cell)
Z:
1
Morphology:
Elongated [100] and flattened (100). Dominant faces are (100} and {010}; ten other forms were noted in type material.
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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View
CIF File Best | x | y | z | a | b | c
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Rotation
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Labels
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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) |
|---|---|---|---|---|---|---|---|
| 0009977 | Demesmaekerite | Ginderow D, Cesbron F (1983) Structure de la demesmaekerite,Pb2Cu5(SeO3)6(UO2)2(OH)6*2H2O Acta Crystallographica C39 824-827 |  | 1983 | Musoni, Kolwezi, Shaba, Zaire | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 2.97 Å | (FFF) |
| 5.42 Å | (FF) |
| 5.89 Å | (F) |
| 3.34 Å | (F) |
| 5.14 Å | (mF) |
| 4.72 Å | (mF) |
| 4.67 Å | (mF) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 47a : [Near-surface hydration of prior minerals] | |
| 47d : [Arsenates, antimonates, selenates, bismuthinates] | |
| 47f : [Uranyl (U⁶⁺) minerals] |
Type Occurrence of Demesmaekerite
Place of Conservation of Type Material:
Université de Paris.
Musée de Minéralogie, Ecole des Mines de Paris.
Muséum national d'Histoire naturelle, Paris.
National History Museum, London.
Musée de Minéralogie, Ecole des Mines de Paris.
Muséum national d'Histoire naturelle, Paris.
National History Museum, London.
Associated Minerals at Type Locality:
Synonyms of Demesmaekerite
Other Language Names for Demesmaekerite
Common Associates
Associations Based on Photo Data:
| 30 photos of Demesmaekerite associated with Malachite | Cu2(CO3)(OH)2 |
| 13 photos of Demesmaekerite associated with Derriksite | Cu4(UO2)(SeO3)2(OH)6 |
| 12 photos of Demesmaekerite associated with Guilleminite | Ba(UO2)3(SeO3)2O2 · 3H2O |
| 11 photos of Demesmaekerite associated with Chalcomenite | CuSeO3 · 2H2O |
| 8 photos of Demesmaekerite associated with Digenite | Cu9S5 |
| 6 photos of Demesmaekerite associated with Kasolite | Pb(UO2)(SiO4) · H2O |
| 2 photos of Demesmaekerite associated with Hematite | Fe2O3 |
| 2 photos of Demesmaekerite associated with Marthozite | Cu2+(UO2)3(SeO3)2O2 · 8H2O |
| 2 photos of Demesmaekerite associated with Vandenbrandeite | Cu(UO2)(OH)4 |
| 1 photo of Demesmaekerite associated with Quartz | SiO2 |
Related Minerals - Strunz-mindat Grouping
| 4.JJ. | Kristekite | Cu2(H2O)4(UO2)(SeO3)3 · 4H2O |
| 4.JJ.X | Larisaite | Na(H3O)(UO2)3(SeO3)O2 · 4H2O |
| 4.JJ. | Borzęckiite | Pb(UO2)3(SeO3)2O2 · 3H2O |
| 4.JJ. | Petermegawite | Al6(Se4+O3)3[SiO3(OH)](OH)9 · 10H2O |
| 4.JJ. | Amurselite | (NH4)2(UO2)5(SeO3)3O2(OH)2(H2O) · 8H2O |
| 4.JJ.05 | Marthozite | Cu2+(UO2)3(SeO3)2O2 · 8H2O |
| 4.JJ.10 | Guilleminite | Ba(UO2)3(SeO3)2O2 · 3H2O |
| 4.JJ.15 | Piretite | Ca(UO2)3(SeO3)2(OH)4 · 4H2O |
| 4.JJ.25 | Haynesite | (UO2)3(Se4+O3)2(OH)2 · 5H2O |
| 4.JJ.30 | Favreauite | PbBiCu6O4(SeO3)4(OH) · H2O |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 21.9179% | 5,479,475 | α, β, γ |
| Thorium (Th) | 0.0000% | 0 | α, β, γ |
| Potassium (K) | 0.0000% | 0 | 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
Notes:
Radioactive
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 Demesmaekerite
mindat.org URL:
https://www.mindat.org/min-1259.html
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Please feel free to link to this page.
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References for Demesmaekerite
Reference List:
Cesbron, Fabien; Bachet, Bernard; Oosterbosch, Robert (1965) La demesmaekerite, sélénite hydraté d'uranium, cuivre et plomb. Bulletin de Minéralogie, 88 (3). 422-425 doi:10.3406/bulmi.1965.5874
Ginderow, D., Cesbron, F. (1983) Structure de la demesmaekerite, Pb2Cu5(SeO3)6(UO2)2(OH)6·2H2O. Acta Crystallographica Section C Crystal Structure Communications, 39 (7) 824-827 doi:10.1107/s0108270183006496
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., Reddy, B. Jagannadha, Dickfos, Marilla J. (2008) An Application of near Infrared and Mid-Infrared Spectroscopy to the Study of Uranyl Selenite Minerals: Derriksite, Demesmaekerite, Guilleminite and Haynesite. Journal of Near Infrared Spectroscopy, 16 (5) 455-469 doi:10.1255/jnirs.813
Localities for Demesmaekerite
Showing 4 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.
Czech Republic | |
| Plášil et al. (2026) |
| Pauliš et al. (2006) +2 other references |
DR Congo (TL) | |
| Cesbron et al. (1965) +2 other references |
Spain | |
| Castillo-Oliver et al. (2019) |
Quick NavTopAbout DemesmaekeriteUnique IdentifiersIMA Classification Classification Mineral SymbolsPhysical Properties Optical Data Chemistry Crystallography Crystal StructureX-Ray Powder DiffractionGeological EnvironmentType Occurrence SynonymsOther LanguagesCommon AssociatesStrunz-MindatRadioactivityOther InformationInternet Links References Localities Locality List
Musonoi Mine, Kolwezi, Mutshatsha, Lualaba, DR Congo