Umohoite
A valid IMA mineral species - grandfathered
This page is currently not sponsored. Click here to sponsor this page.
About Umohoite
Formula:
(UO2)MoO4 · 2H2O
Colour:
Black, blue-black, dark green
Lustre:
Vitreous
Hardness:
2
Specific Gravity:
4.53 - 4.66
Crystal System:
Triclinic
Name:
The name reflects its composition: uranyl (U), molybdate (Mo) and water (H2O).
This page provides mineralogical data about Umohoite.
Unique Identifiers
Mindat ID:
4093
Long-form identifier:
mindat:1:1:4093:4
IMA Classification of Umohoite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
(U6+O2)Mo6+O4·2H2O
Classification of Umohoite
4.GC.10
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
G : Uranyl Hydroxides
C : With additional cations; with mainly UO2(O,OH)6 hexagonal polyhedra
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
G : Uranyl Hydroxides
C : With additional cations; with mainly UO2(O,OH)6 hexagonal polyhedra
49.2.2.1
49 : HYDRATED MOLYBDATES AND TUNGSTATES
2 : Hydrated Normal Molybdates and Tungstates
49 : HYDRATED MOLYBDATES AND TUNGSTATES
2 : Hydrated Normal Molybdates and Tungstates
27.3.8
27 : Sulphites, Chromates, Molybdates and Tungstates
3 : Molybdates
27 : Sulphites, Chromates, Molybdates and Tungstates
3 : Molybdates
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 |
|---|---|---|
| Umo | 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 Umohoite
Vitreous
Transparency:
Opaque
Colour:
Black, blue-black, dark green
Hardness:
2 on Mohs scale
Cleavage:
Perfect
Perfect on {001}
Perfect on {001}
Density:
4.53 - 4.66 g/cm3 (Measured) 4.49(3) g/cm3 (Calculated)
Optical Data of Umohoite
Type:
Biaxial (-)
RI values:
nα = 1.66 nβ = 1.831 nγ = 1.915
2V:
Measured: 65° , Calculated: 64°
Max. Birefringence:
δ = 0.255
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.
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:
weak r>v
Pleochroism:
Visible
Comments:
X= dark blue
Y= pale blue
Z= olive-green
Y= pale blue
Z= olive-green
Chemistry of Umohoite
Mindat Formula:
(UO2)MoO4 · 2H2O
Element Weights:
Elements listed:
Crystallography of Umohoite
Crystal System:
Triclinic
Cell Parameters:
a = 14.6 Å, b = 7.5 Å, c = 6.38 Å
β = 99.08°
β = 99.08°
Ratio:
a:b:c = 1.947 : 1 : 0.851
Unit Cell V:
nan ų (Calculated from Unit Cell)
Z:
4
Morphology:
Tabular plates, rosettes, massive, disseminated, thin veinlets
Comment:
pseudorhombohedral
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Show
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
Remove metal-metal sticks
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
Remove metal-metal sticks
Display Options
Black Background | White Background
Perspective On | Perspective Off
2D | Stereo | Red-Blue | Red-Cyan
Black Background | White Background
Perspective On | Perspective Off
2D | Stereo | Red-Blue | Red-Cyan
View
CIF File Best | x | y | z | a | b | c
CIF File Best | x | y | z | a | b | c
Rotation
Stop | Start
Stop | Start
Labels
Console Off | On | Grey | Yellow
Console Off | On | Grey | Yellow
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) |
|---|---|---|---|---|---|---|---|
| 0005655 | Umohoite | Krivovichev S V, Burns P C (2000) Crystal chemistry of uranyl molybdates. 1. The structure and formula of umohoite The Canadian Mineralogist 38 717-726 |  | 2000 | 0 | 293 | |
| 0017795 | Umohoite | Makarov E S, Anikina L I (1963) Crystal structure of umohoite (UMoO6(H2O)2)*2H2O Geochemistry 1 14-21 | 1963 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 4.13 Å | (100) |
| 3.20 Å | (50) |
| 3.15 Å | (40) |
| 12.2 Å | (30) |
| 6.18 Å | (30) |
| 2.07 Å | (30) |
| 3.11 Å | (20) |
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:
Secondary mineral in sediment hosted uranium deposits in zone above water table.
Type Occurrence of Umohoite
General Appearance of Type Material:
Small flat black flakes with triangular markings, in veinlets, and in disseminated grains.
Place of Conservation of Type Material:
No designated type material.
Associated Minerals at Type Locality:
Other Language Names for Umohoite
Common Associates
Associations Based on Photo Data:
| 46 photos of Umohoite associated with Calcurmolite | Ca[(UO2)3(MoO4)2(OH)4](H2O)~5.0 |
| 27 photos of Umohoite associated with Parauranophane | Ca(UO2)2(SiO3OH)2 · 5H2O |
| 17 photos of Umohoite associated with Uranophane | Ca(UO2)2(SiO3OH)2 · 5H2O |
| 12 photos of Umohoite associated with Zeunerite | Cu(UO2)2(AsO4)2 · 12H2O |
| 9 photos of Umohoite associated with Iriginite | (UO2)Mo2O7 · 3H2O |
| 9 photos of Umohoite associated with Metaschoepite | (UO2)8O2(OH)12 · 10H2O |
| 9 photos of Umohoite associated with Baryte | BaSO4 |
| 8 photos of Umohoite associated with Hydronováčekite | Mg(UO2)2(AsO4)2 · 12H2O |
| 5 photos of Umohoite associated with Tyrolite | Ca2Cu9(AsO4)4(CO3)(OH)8 · 11H2O |
| 3 photos of Umohoite associated with Nováčekite | Mg(UO2)2(AsO4)2 · 10H2O |
Related Minerals - Strunz-mindat Grouping
| 4.GC. | Bobfinchite | Na[(UO2)8O3(OH)11] · 10H2O |
| 4.GC.05 | Clarkeite | (Na,Ca,Pb)(UO2)O(OH) · 0-1H2O |
| 4.GC.15 | Spriggite | Pb3(UO2)6O8(OH)2 · 3H2O |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 51.0774% | 12,769,350 | 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:
HNO3 1:1 - effervesces, then turns yellow and yellow-brown.
FeCl2 20% - etches mineral strongly.
Aqua Regia - quickly and strongly etched.
HCl 1:1, KOH 40%, HgCl2 5%, H2O2, HCl Dil. 10% U.S.P. - all negative.
FeCl2 20% - etches mineral strongly.
Aqua Regia - quickly and strongly etched.
HCl 1:1, KOH 40%, HgCl2 5%, H2O2, HCl Dil. 10% U.S.P. - all negative.
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 Umohoite
mindat.org URL:
https://www.mindat.org/min-4093.html
Please feel free to link to this page.
Please feel free to link to this page.
Search Engines:
External Links:
Mineral Dealers:
References for Umohoite
Reference List:
Coleman, Robert G.; Appleman, Daniel E. (1957) Umohoite from the Lucky MC Mine, Wyoming. American Mineralogist, 42 (9-10). p.657-660.
Coleman, Robert Griffin; Appleman, Daniel E. (1957) Umohoite from the Lucky MC Mine, Fremont County, Wyoming. Trace Elements Investigations 657. US Geological Survey doi:10.3133/tei657
Krivovichev, S. V., Burns, P. C. (2000) Crystal chemistry of uranyl molybdates. I. The structure and formula of umohoite. The Canadian Mineralogist, 38 (3) 717-726 doi:10.2113/gscanmin.38.3.717
Localities for Umohoite
Showing 24 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.
DR Congo | |
| 304 [286-287]. +2 other references |
Egypt | |
| Bisher (2012) |
France | |
| - (1998) |
| [MinRec 25:209 +2 other references |
| Henriot et al. (1998) |
Germany | |
| Desor (08/2020) |
| Rée et al. (1974) |
Indonesia | |
| Setiawan I et al. (2014) |
Kazakhstan | |
| Pekov (1998) +1 other reference |
Romania | |
| Szakáll (2002) |
| Szakáll (2002) | |
Slovakia | |
| Števko M. (2022) +1 other reference |
USA | |
| Anthony et al. (1995) |
| Bollin & Kerr (1958) +3 other references | |
| Northrop et al. (1996) +1 other reference |
| Smith (1991) |
| Bomber et al. (1986) | |
| Nikischer (2024) |
| - (2005) |
| Page et al. (1956) +2 other references | |
| Bullock (1981) | |
| Brophy et al. (1953) +1 other reference |
| - (2005) |
| Coleman et al. (1957) +3 other references |
Quick NavTopAbout UmohoiteUnique IdentifiersIMA Classification Classification Mineral SymbolsPhysical Properties Optical Data Chemistry Crystallography Crystal StructureX-Ray Powder DiffractionGeological EnvironmentType Occurrence Other LanguagesCommon AssociatesStrunz-MindatRadioactivityOther InformationInternet Links References Localities Locality List
Kyzylsai Mo-U deposit, Chu-Ili Mountains, Ulytau District, Ulytau Region, Kazakhstan