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Hubbardite
A valid IMA mineral species
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About Hubbardite
Formula:
Mg(H2O)6[(UO2)2O(OH)(SO4)]2 · 8H2O
Colour:
yellow in color but sometimes appears dark brown
Lustre:
Vitreous
Hardness:
2½
Specific Gravity:
3.59
Crystal System:
Orthorhombic
Name:
For type locality
Unique Identifiers
Mindat ID:
494672
Long-form identifier:
mindat:1:1:494672:0
Classification of Hubbardite
The zippeite-type sheet
The zippeite-like uranyl sulfate sheet topology found in hubbardite.
IMA Classification of Hubbardite
Approved
IMA Formula:
Mg(H2O)6[(U6+O2)2O(OH)(S6+O4)]2·8H2O
Approval year:
2025
7.EC.15
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
E : Uranyl sulfates
C : With medium-sized and large cations
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
E : Uranyl sulfates
C : With medium-sized and large cations
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 |
|---|---|---|
| Hbb | 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 Hubbardite
Vitreous
Transparency:
Transparent
Colour:
Yellow in color but sometimes appears dark brown
Streak:
Pale-yellow
Hardness:
2½ on Mohs scale
Tenacity:
Flexible
Fracture:
Step-Like
Density:
3.59(5) g/cm3 (Measured) 3.546 g/cm3 (Calculated)
Optical Data of Hubbardite
Type:
Biaxial (-)
RI values:
nα = 1.570(5) nβ = 1.625(5) nγ = 1.646(5)
2V:
Measured: 62° (2)
Max. Birefringence:
δ = 0.076
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:
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:
r
Orientation:
X = c, Y = b, Z = a,
Pleochroism:
Visible
Comments:
X light yellow, Y yellow, Z brownish yellow; X
Chemistry of Hubbardite
Mindat Formula:
Mg(H2O)6[(UO2)2O(OH)(SO4)]2 · 8H2O
Element Weights:
Crystallography of Hubbardite
Crystal System:
Orthorhombic
Class (H-M):
mmm(2/m2/m2/m) - Dipyramidal
Space Group:
Fddd
Setting:
Fddd
Cell Parameters:
a = 8.870(2) Å, b = 34.183(7) Å, c = 39.377(9) Å
Ratio:
a:b:c = 0.259 : 1 : 1.152
Unit Cell V:
11,939.23 ų (Calculated from Unit Cell)
Z:
16
Twinning:
none
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 9.659 Å | (100) |
| 4.851 Å | (21) |
| 4.215 Å | (15) |
| 3.448 Å | (48) |
| 3.078 Å | (24) |
| 2.735 Å | (11) |
| 2.152 Å | (12) |
| 1.744 Å | (14) |
Type Occurrence of Hubbardite
General Appearance of Type Material:
Crystals are plates up to about 0.3 mm in diameter, commonly forming subparallel or divergent aggregates. Crystals are flattened on {001} and exhibit the forms {100}, {001} and {140}
Place of Conservation of Type Material:
Type material is deposited in the collections of the Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA, catalogue number 76119 (holotype), 76120 and 76121 (cotype)
Geological Setting of Type Material:
forms from the oxidation of uraninite-montroseite-corvusite assemblages in a moist environment.
Associated Minerals at Type Locality:
Synonyms of Hubbardite
Other Language Names for Hubbardite
Dutch:Hubbardiet
Relationship of Hubbardite to other Species
Structurally related to group(s):
| Zippeite Group | A group of metal uranyl sulphates with layered structures. |
Common Associates
Related Minerals - Strunz-mindat Grouping
| 7.EC. | Nitscheite | (NH4)2[(UO2)2(SO4)3(H2O)2] · 3H2O |
| 7.EC. | Beshtauite | (NH4)2(UO2)(SO4)2 · 2H2O |
| 7.EC. | Oldsite-(K) | K2Fe2+[(UO2)(SO4)2]2(H2O)8 |
| 7.EC. | Adolfpateraite | K(UO2)(SO4)(OH)(H2O) |
| 7.EC. | Libbyite | (NH4)2(Na2◻)[(UO2)2(SO4)3(H2O)]2 · 7H2O |
| 7.EC. | Seaborgite | LiK2Na6(UO2)(SO4)5(SO3OH)(H2O) |
| 7.EC.05 | Zinczippeite | Zn(UO2)2(SO4)O2 · 3.5H2O |
| 7.EC.05 | Zippeite | K3(UO2)4(SO4)2O3(OH) · 3H2O |
| 7.EC.05 | Cobaltzippeite | Co(UO2)2(SO4)O2 · 3.5H2O |
| 7.EC.05 | Nickelzippeite | Ni2(UO2)6(SO4)3(OH)10 · 16H2O |
| 7.EC.05 | Redcanyonite | (NH4)2Mn[(UO2)4O4(SO4)2](H2O)4 |
| 7.EC.05 | Natrozippeite | Na5(UO2)8(SO4)4O5(OH)3 · 12H2O |
| 7.EC.05 | Magnesiozippeite | Mg(UO2)2(SO4)O2 · 3.5H2O |
| 7.EC.05 | Ammoniozippeite | (NH4)2[(UO2)2(SO4)O2] · H2O |
| 7.EC.05 | Plavnoite | K0.8Mn0.6[(UO2)2O2(SO4)] · 3.5H2O |
| 7.EC.10 | Rabejacite | Ca(UO2)4(SO4)2(OH)6 · 6H2O |
| 7.EC.10 | Svornostite-(NH4) | (NH4)2Mg(UO2)2(SO4)4(H2O)8 |
| 7.EC.10 | Svornostite-(K) | K2Mg[(UO2)(SO4)2]2(H2O)8 |
| 7.EC.15 | Sejkoraite-(Y) | Y2(UO2)8(SO4)4O6(OH)2 · 26H2O |
| 7.EC.15 | Marécottite | Mg3(UO2)8(SO4)4O6(OH)2 · 28H2O |
| 7.EC.20 | Pseudojohannite | Cu3(UO2)4(SO4)2O4(OH)2 · 12H2O |
| 7.EC.40 | Bluelizardite | Na7(UO2)(SO4)4Cl(H2O)2 |
| 7.EC.45 | Meisserite | Na5(UO2)(SO4)3(SO3OH)(H2O) |
| 7.EC.45 | Fermiite | Na4(UO2)(SO4)3 · 3H2O |
| 7.EC.45 | Oppenheimerite | Na2(UO2)(SO4)2 · 3H2O |
| 7.EC.50 | Feynmanite | Na(UO2)(SO4)(OH) · 3.5H2O |
| 7.EC.50 | Plášilite | Na(UO2)(SO4)(OH) · 2H2O |
| 7.EC.55 | Geschieberite | K2(UO2)(SO4)2 · 2H2O |
| 7.EC.60 | Ottohahnite | Na6(UO2)2(SO4)5(H2O)7 · 1.5H2O |
| 7.EC.65 | Péligotite | Na6(UO2)(SO4)4 · 4H2O |
| 7.EC.70 | Klaprothite | Na6(UO2)(SO4)4 · 4H2O |
| 7.EC.75 | Lussierite | Na10[(UO2)(SO4)4](SO4)2 · 3(H2O) |
| 7.EC.80 | Navrotskyite | K2Na10(UO2)3(SO4)9 · 2H2O |
| 7.EC.85 | Pseudomeisserite-(NH4) | (NH4)2Na4[(UO2)2(SO4)5] · 4H2O |
| 7.EC.90 | Wetherillite | Na2Mg(UO2)2(SO4)4 · 18H2O |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 58.9630% | 14,740,750 | 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 Hubbardite
none
Other Information
Notes:
At room temperature, hubbardite is slowly soluble in dilute HCl. The mineral very slowly decomposes (loses birefringence) in H2O.
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 Hubbardite
mindat.org URL:
https://www.mindat.org/min-494672.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Hubbardite
Localities for Hubbardite
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.
USA (TL) | |
| Kampf et al. (2025) +1 other reference |
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Hubbard Homestead Mine, Beaver Mesa, Gateway Mining District, Mesa County, Colorado, USA