Bobfinchite
A valid IMA mineral species
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About Bobfinchite
Robert Finch
Formula:
Na[(UO2)8O3(OH)11] · 10H2O
Colour:
yellow
Lustre:
Vitreous
Hardness:
2
Specific Gravity:
5.044 (Calculated)
Crystal System:
Orthorhombic
Name:
Named in honor of Robert Finch (b. 1958), an expert in the area of nuclear waste at Sandia National Laboratories, New Mexico, USA and a crystallographer. He has solved the crystal structure of several uranyl minerals.
Type Locality:
Unique Identifiers
Mindat ID:
55374
Long-form identifier:
mindat:1:1:55374:8
IMA Classification of Bobfinchite
Approved
IMA Formula:
Na[(U6+O2)8O3(OH)11]·10H2O
Approval year:
2021
Approval history:
IMA No. 2020-082
Classification of Bobfinchite
4.GC.
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
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 |
|---|---|---|
| Bfc | 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 Bobfinchite
Vitreous
Transparency:
Transparent, Translucent
Colour:
Yellow
Streak:
Pale yellow
Hardness:
2 on Mohs scale
Tenacity:
Brittle
Cleavage:
Very Good
{100}
{100}
Fracture:
Irregular/Uneven, Step-Like
Density:
5.044 g/cm3 (Calculated)
Optical Data of Bobfinchite
Type:
Biaxial (-)
RI values:
nα = 1.690(5) nβ = 1.7205(5) nγ = 1.730(5)
2V:
Measured: 55° , Calculated: 59.1°
Max. Birefringence:
δ = 0.040
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.
Pleochroism:
Visible
Comments:
X nearly colourless, Y yellow, Z yellow; X < Y ≈ Z
Chemistry of Bobfinchite
Mindat Formula:
Na[(UO2)8O3(OH)11] · 10H2O
Element Weights:
Elements listed:
Crystallography of Bobfinchite
Crystal System:
Orthorhombic
Class (H-M):
mmm(2/m2/m2/m) - Dipyramidal
Space Group:
Pbcn
Setting:
Pbcn
Cell Parameters:
a = 14.6249(9) Å, b = 14.0389(10) Å, c = 16.6923(10) Å
Ratio:
a:b:c = 1.042 : 1 : 1.189
Unit Cell V:
3,427.22 ų (Calculated from Unit Cell)
Z:
4
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 7.337 Å | (100) |
| 3.658 Å | (21) |
| 3.590 Å | (50) |
| 3.516 Å | (22) |
| 3.229 Å | (63) |
| 3.176 Å | (36) |
| 2.568 Å | (20) |
| 2.013 Å | (23) |
Type Occurrence of Bobfinchite
General Appearance of Type Material:
lozenge-shaped discs up to 0.3 mm wide
Place of Conservation of Type Material:
Mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA, catalogue number 75146
Geological Setting of Type Material:
secondary mineral in uranium deposit
Associated Minerals at Type Locality:
Synonyms of Bobfinchite
Other Language Names for Bobfinchite
Dutch:Bobfinchiet
German:Bobfinchit
Common Associates
Associations Based on Photo Data:
| 1 photo of Bobfinchite associated with Natrozippeite | Na5(UO2)8(SO4)4O5(OH)3 · 12H2O |
| 1 photo of Bobfinchite associated with Andersonite | Na2Ca(UO2)(CO3)3 · 5.33H2O |
| 1 photo of Bobfinchite associated with Gypsum | CaSO4 · 2H2O |
Related Minerals - Strunz-mindat Grouping
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 73.2835% | 18,320,875 | 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 Bobfinchite
yellow fluorescence under 365 nm ultraviolet illumination
Other Information
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 Bobfinchite
mindat.org URL:
https://www.mindat.org/min-55374.html
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Please feel free to link to this page.
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References for Bobfinchite
Localities for Bobfinchite
Showing 3 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.
Spain | |
| Hamza Ilhan Sito Collection |
USA | |
| Carnegie Museum of Natural History ... |
| Miyawaki et al. (2021) +1 other reference |
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Burro Mine, San Miguel County, Colorado, USA