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Boltwoodite

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Rössing Mine, Arandis, Swakopmund District, Erongo Region, Namibia
© Stephan Wolfsried

Show Boltwoodite Photos (84)
Formula:
(K,Na)(UO
 
2
)[HSiO
 
4
] · 0.5H
 
2
O
System:MonoclinicColour:Pale yellow, orange ...
Lustre:Sub-Vitreous, Waxy, SilkyHardness:3½ - 4
Name:
For Bertram Borden Boltwood (1870-1927), radiochemist at Yale University, New Haven, Connecticut, USA. Named by Clifford Frondel and Jun Ito.
Isostructural with:Uranophane Group


Rod-like to acicular yellow crystals in radial groups

Classification of Boltwoodite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:8/B.34-60
Nickel-Strunz 10th (pending) edition ID:9.AK.15

9 : SILICATES (Germanates)
A : Nesosilicates
K : Uranyl neso- and polysilicates
Dana 8th edition ID:53.3.1.5

53 : NESOSILICATES Insular SiO4 Groups and Other Anions or Complex Cations
3 : Insular SiO4 Groups and Other Anions of Complex Cations with (UO2)
Hey's CIM Ref.:14.16.6

14 : Silicates not Containing Aluminum
16 : Silicates of U
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Type Occurrence of Boltwoodite

Type Locality:Pick's Delta Mine (Delta Mine; Pick's Mine), Delta, San Rafael District (San Rafael Swell), Emery Co., Utah, USA
Year of Discovery:1956

Occurrences of Boltwoodite

Geological Setting:Alteration zone around uranium deposits.

Physical Properties of Boltwoodite

Lustre:Sub-Vitreous, Waxy, Silky
Diaphaneity (Transparency):Translucent
Comment:Aggregates vitreous to silky, dull to earthy in pseudomorphs
Colour:Pale yellow, orange yellow
Streak:White
Hardness (Mohs):3½ - 4
Tenacity:Brittle
Cleavage:Perfect
Perfect on {010}
imperfect on {001}
Fracture:Irregular/Uneven
Density (measured):4.7 g/cm3
Density (calculated):4.46 g/cm3

Crystallography of Boltwoodite

Crystal System:Monoclinic
Class (H-M):2 - Sphenoidal
Space Group:P21 {P1 1 21} {P21} {P1 21 1}
Cell Parameters:a = 7.073(2) Å, b = 7.064(1) Å, c = 6.638(1) Å
β = 105.45°
Ratio:a:b:c = 1.001 : 1 : 0.94
Unit Cell Volume:V 319.67 ų (Calculated from Unit Cell)
Z:2
Morphology:Radiating acicular to fibrous crystals, also earthy pseudomorphs of uranium minerals
X-Ray Powder Diffraction:
d-spacingIntensity
6.81 (10)
6.40 (50)
3.54 (70)
3.40 (90)
2.95 (80)
2.91 (70)
1.900 (60)
1.764 (60)
Comments:35-490

Optical Data of Boltwoodite

Type:Biaxial (-)
RI values: nα = 1.668 - 1.670 nβ = 1.695 - 1.696 nγ = 1.698 - 1.703
Birefringence:0.007-0.008
Maximum Birefringence:δ = 0.030 - 0.033

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:High
Dispersion:r > v or r < v
Pleochroism:Weak
Comments:X= colorless
Y=Z= yellow

Chemical Properties of Boltwoodite

Formula:
(K,Na)(UO
 
2
)[HSiO
 
4
] · 0.5H
 
2
O
Essential elements:H, K, O, Si, U
All elements listed in formula:H, K, Na, O, Si, U
Common Impurities:Fe,Ca,Na

Relationship of Boltwoodite to other Species

Member of Group:
Uranophane Group:
Related Minerals - Nickel-Strunz Grouping):

- +
9.AK.05Soddyite
(UO
 
2
)
 
2
SiO
 
4
·2H
 
2
O
9.AK.10Cuprosklodowskite
Cu(UO
 
2
)
 
2
[HSiO
 
4
]
 
2
 · 6H
 
2
O
9.AK.10Oursinite
(Co,Mg)(UO
 
2
)
 
2
[HSiO
 
4
]
 
2
 · 6H
 
2
O
9.AK.10Sklodowskite
Mg(UO
 
2
)
 
2
[HSiO
 
4
]
 
2
 · 5H
 
2
O
9.AK.15Kasolite
Pb(UO
 
2
)[SiO
 
4
] · H
 
2
O
9.AK.15Natroboltwoodite
(H
 
3
O)(Na,K)UO
 
2
SiO
 
4
·H
 
2
O
9.AK.15Uranophane
Ca(UO
 
2
)
 
2
[HSiO
 
4
]
 
2
 · 5H
 
2
O
9.AK.15Beta-Uranophane
9.AK.20Swamboite
UH
 
6
(UO
 
2
)
 
6
(SiO
 
4
)
 
6
·30H
 
2
O
9.AK.25Haiweeite
Ca(UO
 
2
)
 
2
[Si
 
5
O
 
12
(OH)
 
2
]·4.5H
 
2
O
9.AK.25Metahaiweeite
Ca(UO
 
2
)
 
2
Si
 
6
O
 
15
·nH
 
2
O
9.AK.25Ranquilite
9.AK.30Weeksite
K
 
2
(UO
 
2
)
 
2
(Si
 
2
O
 
5
)
 
3
·4H
 
2
O
9.AK.30Coutinhoite
Th
 
x
Ba
 
(1-2x)
(UO
 
2
)
 
2
Si
 
5
O
 
13
·(H
 
2
O)
 
1+y
 (0 < x < 0.5 and 0 < y < (2+x))
9.AK.35Ursilite
(Mg,Ca)
 
4
(UO
 
2
)
 
4
(Si
 
2
O
 
5
)
 
5.5
(OH)
 
5
·13H
 
2
O
9.AK.35Magnioursilite
Mg
 
4
(UO
 
2
)
 
4
(Si
 
2
O
 
5
)
 
5
(OH)
 
6
·20H
 
2
O
9.AK.35Calcioursilite
Ca
 
4
(UO
 
2
)
 
4
(Si
 
2
O
 
5
)
 
5
(OH)
 
6
·15H
 
2
O
9.AK.40Uranosilite
UO
 
3
 · 7SiO
 
2
Related Minerals - Hey's Index Grouping:

- +
14.16.1Uranosilite
UO
 
3
 · 7SiO
 
2
14.16.2Coffinite
(U,Th)[(OH)
 
4x
|(SiO
 
4
)
 
1-x
]
14.16.3Soddyite
(UO
 
2
)
 
2
SiO
 
4
·2H
 
2
O
14.16.4Swamboite
UH
 
6
(UO
 
2
)
 
6
(SiO
 
4
)
 
6
·30H
 
2
O
14.16.5Weeksite
K
 
2
(UO
 
2
)
 
2
(Si
 
2
O
 
5
)
 
3
·4H
 
2
O
14.16.7Natroboltwoodite
(H
 
3
O)(Na,K)UO
 
2
SiO
 
4
·H
 
2
O
14.16.8Cuprosklodowskite
Cu(UO
 
2
)
 
2
[HSiO
 
4
]
 
2
 · 6H
 
2
O
14.16.9Sklodowskite
Mg(UO
 
2
)
 
2
[HSiO
 
4
]
 
2
 · 5H
 
2
O
14.16.10Uranophane
Ca(UO
 
2
)
 
2
[HSiO
 
4
]
 
2
 · 5H
 
2
O
14.16.11β-Uranophane
Ca(UO
 
2
)
 
2
[HSiO
 
4
]
 
2
 · 5H
 
2
O
14.16.12Haiweeite
Ca(UO
 
2
)
 
2
[Si
 
5
O
 
12
(OH)
 
2
]·4.5H
 
2
O
14.16.13Metahaiweeite
Ca(UO
 
2
)
 
2
Si
 
6
O
 
15
·nH
 
2
O
14.16.14Thorogummite
(Th,U)[(OH)
 
4x
|(SiO
 
4
)
 
1-x
]
14.16.15Steacyite
([ ],K)(Na,Ca)
 
2
(Th,U)[Si
 
8
O
 
20
]
14.16.16Ekanite
(Ca,Fe
2+
 
,Pb)
 
2
(Th,U)[Si
 
8
O
 
20
]
14.16.17Kasolite
Pb(UO
 
2
)[SiO
 
4
] · H
 
2
O
14.16.18 Orlite
Pb
 
3
(UO
 
2
)
 
3
(Si
 
2
O
 
7
)
 
2
·6H
 
2
O
14.16.19Oursinite
(Co,Mg)(UO
 
2
)
 
2
[HSiO
 
4
]
 
2
 · 6H
 
2
O

Other Names for Boltwoodite

Other Languages:
German:Boltwoodit
Russian:Болтвудит
Spanish:Boltwoodita

Other Information

Health Warning:Contains uranium - always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest. Avoid prolonged exposure in proximity of the body. Store away from inhabited areas.

References for Boltwoodite

Reference List:American Mineralogist: 46: 12-25.

American Mineralogist: 66: 610-625.

Burns, P.C. (1998) The structure of boltwoodite and implications of solid-solution towards sodium boltwoodite. Canadian Mineralogist: 36: 1069-1075.

Burns, P.C. (2005) U 6+ minerals and inorganic compounds: insights into an expanded structural hierarchy of crystal structures. Canadian Mineralogist: 43: 1839-1894.

Internet Links for Boltwoodite

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  • Raman and XRD data at RRUFF project
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