Znucalite
A valid IMA mineral species
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About Znucalite
Formula:
Zn10Ca0.83(UO2)0.83(CO3)4(OH)15.31(H2O)5.48
The above formula is the structural formula; formerly given as Zn12Ca(UO2)(CO3)3(OH)22·4H2O
Colour:
White to light yellow
Lustre:
Silky
Specific Gravity:
3.01 - 3.1
Crystal System:
Monoclinic
Name:
Named in 1990 by Petr Ondruš, František Veselovský, and R. Rybka for its chemical composition containing Zinc (Zn), Uranium (U) and Calcium (Ca).
The layered structure is based on [Zn10(OH)14(CO3)2] double sheet, with both octahedral and tetrahedral Zn. The thick interlayer bears Ca ions and uranyl and water groups. Ordering of Ca and U varies which is suggested to cause issues with solving the structure.
Unique Identifiers
Mindat ID:
4428
Long-form identifier:
mindat:1:1:4428:4
IMA Classification of Znucalite
Approved
IMA Formula:
Zn2+10Ca(U6+O2)(CO3)4(OH)16(H2O)5
Approval year:
1989
First published:
1990
Classification of Znucalite
5.ED.45
5 : CARBONATES (NITRATES)
E : Uranyl Carbonates
D : UO2:CO3 = 1:3
5 : CARBONATES (NITRATES)
E : Uranyl Carbonates
D : UO2:CO3 = 1:3
16b.7.14.1
16b : HYDRATED CARBONATES CONTAINING HYDROXYL OR HALOGEN
7 : Miscellaneous
16b : HYDRATED CARBONATES CONTAINING HYDROXYL OR HALOGEN
7 : Miscellaneous
11.11.20
11 : Carbonates
11 : Carbonates of Cr and U
11 : Carbonates
11 : Carbonates of Cr and 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 |
|---|---|---|
| Znu | 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 Znucalite
Silky
Transparency:
Translucent
Colour:
White to light yellow
Streak:
White
Cleavage:
Perfect
{010}
{010}
Density:
3.01 - 3.1 g/cm3 (Measured) 3.15 g/cm3 (Calculated)
Optical Data of Znucalite
Type:
Biaxial (-)
RI values:
nα = 1.556 - 1.563 nβ = 1.600 nγ = 1.620 - 1.621
2V:
Measured: 50° to 66°, Calculated: 66.4°
Max. Birefringence:
δ = 0.058 - 0.064
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:
strong
Optical Extinction:
Extinction inclined about 9° (type description)
Parallel extinction (Mas d'Alary, France)
Parallel extinction (Mas d'Alary, France)
Comments:
X = c; Y = b; Z = a.
Negative elongation.
Type description gives β = 1.620 and 2V (calculated) = 0.
Negative elongation.
Type description gives β = 1.620 and 2V (calculated) = 0.
Chemistry of Znucalite
Mindat Formula:
Zn10Ca0.83(UO2)0.83(CO3)4(OH)15.31(H2O)5.48
The above formula is the structural formula; formerly given as Zn12Ca(UO2)(CO3)3(OH)22·4H2O
The above formula is the structural formula; formerly given as Zn12Ca(UO2)(CO3)3(OH)22·4H2O
Element Weights:
Crystallography of Znucalite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/m
Setting:
P21/m
Cell Parameters:
a = 10.722(2) Å, b = 6.259(1) Å, c = 25.355(1) Å
β = 101.13(1)°
β = 101.13(1)°
Ratio:
a:b:c = 1.713 : 1 : 4.051
Unit Cell V:
1,669.55 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Crystals are thin lamellar, to 100 µm, in spherical boxworklike aggregates; forms coatings.
From Mas d'Alary, France, crystals are elongate [001] and platy on (010).
From Mas d'Alary, France, crystals are elongate [001] and platy on (010).
Comment:
Cell parameters from Steciuk et al. (2023). They differ significantly from the type description which was thought to be triclinic..
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 25.10 Å | (62) |
| 6.141 Å | (78) |
| 5.650 Å | (54) |
| 3.165 Å | (70) |
| 2.728 Å | (90) |
| 2.708 Å | (100) |
| 2.682 Å | (56) |
| 1.5820 Å | (77) |
| 1.5600 Å | (62) |
| 1.5561 Å | (67) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 47a : [Near-surface hydration of prior minerals] | |
| 47c : [Carbonates, phosphates, borates, nitrates] | |
| 47f : [Uranyl (U⁶⁺) minerals] | |
| Stage 10b: Anthropogenic minerals | <10 Ka |
| 55 : Anthropogenic mine minerals |
Type Occurrence of Znucalite
General Appearance of Type Material:
Porous coatings of saucer-shaped aggregates, up to 10 cm2, some consisting of thin plates averaging 15 x 8 x 0.4 um.
Place of Conservation of Type Material:
1) National Museum, Prague, Czech Republic.
2) Faculty of Natural Sciences of Charles University, Prague, Czech Republic.
3) The Regional Museum, Pribram, Czech Republic.
2) Faculty of Natural Sciences of Charles University, Prague, Czech Republic.
3) The Regional Museum, Pribram, Czech Republic.
Geological Setting of Type Material:
Oxidation product on uraninite-bearing dump material.
Associated Minerals at Type Locality:
Synonyms of Znucalite
Other Language Names for Znucalite
Common Associates
Associations Based on Photo Data:
| 5 photos of Znucalite associated with Hydrozincite | Zn5(CO3)2(OH)6 |
| 5 photos of Znucalite associated with Gypsum | CaSO4 · 2H2O |
| 5 photos of Znucalite associated with Quartz | SiO2 |
| 4 photos of Znucalite associated with Calcite | CaCO3 |
| 2 photos of Znucalite associated with Dolomite | CaMg(CO3)2 |
| 2 photos of Znucalite associated with Pyrite | FeS2 |
Related Minerals - Strunz-mindat Grouping
| 5.ED. | Szilagyiite | NaCa3(UO2)(CO3)3(SeO3)F(H2O)6 |
| 5.ED. | Pendevilleite-(Y) | Mg2Y3Al(UO2)2(CO3)7(OH)6(H2O)16 |
| 5.ED. | Paramarkeyite | Ca2(UO2)(CO3)3 · 5H2O |
| 5.ED.05 | Bayleyite | Mg2(UO2)(CO3)3 · 18H2O |
| 5.ED.10 | Swartzite | MgCa(UO2)(CO3)3 · 12H2O |
| 5.ED.15 | Albrechtschraufite | Ca4Mg(UO2)2(CO3)6F2 · 17-18H2O |
| 5.ED.20 | Liebigite | Ca2(UO2)(CO3)3 · 11H2O |
| 5.ED.25 | Rabbittite | Ca3Mg3(UO2)2(CO3)6(OH)4 · 18H2O |
| 5.ED.30 | Andersonite | Na2Ca(UO2)(CO3)3 · 5.33H2O |
| 5.ED.35 | Grimselite | K3Na(UO2)(CO3)3 · H2O |
| 5.ED.40 | Widenmannite | Pb2(OH)2[(UO2)(CO3)2] |
| 5.ED.50 | Agricolaite | K4(UO2)(CO3)3 |
| 5.ED.50 | Čejkaite | Na4(UO2)(CO3)3 |
| 5.ED.55 | Línekite | K2Ca3[(UO2)(CO3)3]2 · 8H2O |
| 5.ED.55 | Braunerite | K2Ca(UO2)(CO3)3 · 6H2O |
| 5.ED.60 | Leószilárdite | Na6Mg(UO2)2(CO3)6 · 6H2O |
| 5.ED.65 | Pseudomarkeyite | Ca8(UO2)4(CO3)12 · 21H2O |
| 5.ED.65 | Natromarkeyite | Na2Ca8(UO2)4(CO3)13 · 27H2O |
| 5.ED.65 | Markeyite | Ca9(UO2)4(CO3)13 · 28H2O |
| 5.ED.70 | Paddlewheelite | MgCa5Cu2(UO2)4(CO3)12(H2O)33 |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 13.0809% | 3,270,225 | 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
Fluorescence of Znucalite
Yellow-green fluorescence with SW and LW UV (from type loc).
Not fluorescent (from Mas d'Alary).
Not fluorescent (from Mas d'Alary).
Other Information
Notes:
Readily soluble in acid, with evolution of CO2.
Radioactive.
Raman Spectroscopy confirms, i.a., presence of (several non-equivalent) carbonate groups, OH anions, and water.
Radioactive.
Raman Spectroscopy confirms, i.a., presence of (several non-equivalent) carbonate groups, OH anions, and water.
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 Znucalite
mindat.org URL:
https://www.mindat.org/min-4428.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 Znucalite
Localities for Znucalite
Showing 15 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 |
| Plášil J. et al. (2008) | |
| Desor (09/2025) |
| Ondruš et al. (1990) +1 other reference |
| Hloušek et al. (2002) |
| Möhn et al. (12/2021) | |
| Brent Thorne specimen. SXRD analyzed and acquired from Czechmin (Jakob Plasil) +1 other reference | |
France | |
| Robinson et al. (1992) +1 other reference |
Germany | |
| Möhn et al. (07/2020) |
| Wittern (2001) |
Morocco | |
| Favreau (2026) |
Switzerland | |
| Meisser (2012) |
USA | |
| Ondrush et al. (authors) +3 other references |
| Pete Dunn | |
| Desor (11/2020) |
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Jan Evangelista vein, Svornost Mine, Jáchymov, Karlovy Vary District, Karlovy Vary Region, Czech Republic