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Bettertonite
A valid IMA mineral species
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About Bettertonite
John Betterton
Formula:
[Al6(AsO4)3(OH)9(H2O)5] · 11H2O
Colour:
White
Lustre:
Vitreous, Silky, Pearly
Specific Gravity:
2.02 (Calculated)
Crystal System:
Monoclinic
Name:
Honors John Betterton (b. 1959, London), a museum geologist/mineralogist at Haslemere Educational Museum, Surrey, England, for his extensive contributions to the characterisation of minerals from the Penberthy Croft mine for more than 30 years. Also is an advanced mineral collector and micromounter.
Type Locality:
New structure type, closely related to that of penberthycroftite; both structures are flexible layered type, comprising corner-linked columns of heteropolyhedra.
Chemically similar to liskeardite.
Transforms to penberthycroftyite at relatively low temperatures (see Thermal Behaviour section).
Chemically similar to liskeardite.
Transforms to penberthycroftyite at relatively low temperatures (see Thermal Behaviour section).
Unique Identifiers
Mindat ID:
46516
Long-form identifier:
mindat:1:1:46516:0
IMA Classification of Bettertonite
Approved
IMA Formula:
Al6(As5+O4)3(OH)9·16H2O
Approval year:
2014
First published:
2015
Type description reference:
Classification of Bettertonite
8.DD.
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
D : With only medium-sized cations, (OH, etc.):RO4= 2:1
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
D : With only medium-sized cations, (OH, etc.):RO4= 2:1
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 |
|---|---|---|
| Bet | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Pronunciation of Bettertonite
Pronunciation:
| Play | Recorded by | Country |
|---|---|---|
| Jolyon Ralph | United Kingdom |
Physical Properties of Bettertonite
Vitreous, Silky, Pearly
Transparency:
Translucent
Comment:
Vitreous to pearly, somewhat silky lustre
Colour:
White
Streak:
White
Tenacity:
Flexible
Fracture:
Irregular/Uneven
Density:
2.02 g/cm3 (Calculated)
Optical Data of Bettertonite
Type:
Biaxial (+)
RI values:
nα = 1.511(1) nβ = 1.517(1) nγ = 1.523(1)
Max. Birefringence:
δ = 0.012
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:
Low (negative)
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.
No measured or calculated 2V is on file for this mineral, so the value used here (90°) is estimated from its recorded refractive indices and optic sign, not from a direct 2V measurement.
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.
No measured or calculated 2V is on file for this mineral, so the value used here (90°) is estimated from its recorded refractive indices and optic sign, not from a direct 2V measurement.
Optical Extinction:
X = c; Y = b; Z = a.
Pleochroism:
Non-pleochroic
Chemistry of Bettertonite
Mindat Formula:
[Al6(AsO4)3(OH)9(H2O)5] · 11H2O
Element Weights:
Elements listed:
Crystallography of Bettertonite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/c
Setting:
P21/c
Cell Parameters:
a = 7.773(2) Å, b = 26.991(5) Å, c = 15.867(3) Å
β = 94.22(3)°
β = 94.22(3)°
Ratio:
a:b:c = 0.288 : 1 : 0.588
Unit Cell V:
3,319.89 ų (Calculated from Unit Cell)
Morphology:
Ultrathin rectangular laths, with lateral dimensions generally <20 μm. The laths are flattened on {010} and exhibit the forms {010}, {100} and {001}.
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 13.648 Å | (100) |
| 13.505 Å | (50) |
| 7.805 Å | (50) |
| 7.461 Å | (30) |
| 5.880 Å | (20) |
| 5.622 Å | (12) |
| 3.589 Å | (20) |
| 2.857 Å | (14) |
Reference:
Comments:
From Type Description.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 47a : [Near-surface hydration of prior minerals] | |
| 47d : [Arsenates, antimonates, selenates, bismuthinates] |
Type Occurrence of Bettertonite
General Appearance of Type Material:
As tufts of white, ultrathin (sub-micrometre) rectangular laths, with lateral dimensions generally <20 μm.
Place of Conservation of Type Material:
Cotype material is deposited in the mineralogical collections of Museum Victoria, Melbourne, Victoria, Australia, registration number M53274, and the Natural History Museum, London, UK, registration number BM2014,100
Associated Minerals at Type Locality:
Reference:
Synonyms of Bettertonite
Other Language Names for Bettertonite
Dutch:Bettertoniet
German:Bettertonit
Common Associates
Associations Based on Photo Data:
| 6 photos of Bettertonite associated with Quartz | SiO2 |
| 4 photos of Bettertonite associated with Chamosite | Fe2+5Al(AlSi3O10)(OH)8 |
| 2 photos of Bettertonite associated with Arsenopyrite | FeAsS |
| 1 photo of Bettertonite associated with Pharmacosiderite | KFe3+4(AsO4)3(OH)4 · 6-7H2O |
| 1 photo of Bettertonite associated with Goethite | Fe3+O(OH) |
Related Minerals - Strunz-mindat Grouping
| 8.DD. | Penberthycroftite | [Al6(AsO4)3(OH)9(H2O)5] · 8H2O |
| 8.DD. | Vargite | MnCu2Mn2(AsO4)2(OH)4(H2O)4 |
| 8.DD. | Galeaclolusite | Al6(AsO4)3(OH)9(H2O)4 · 8H2O |
| 8.DD.05 | Luetheite | Cu2Al2(AsO4)2(OH)4 |
| 8.DD.05 | Chenevixite | Cu2Fe3+2(AsO4)2(OH)4 |
| 8.DD.10 | Akrochordite | MnMn2Mn2(AsO4)2(OH)4(H2O)4 |
| 8.DD.10 | Guanacoite | MgCu2Mg2(AsO4)2(OH)4(H2O)4 |
| 8.DD.15 | 'UM1981-32-PO:FeH' | Fe2+Fe3+6(PO4)4-x[PO3(OH)]x(OH)8 · 4H2O |
| 8.DD.15 | Afmite | Al3(OH)4(H2O)3(PO4)(PO3OH) · H2O |
| 8.DD.15 | Aheylite | (Fe2+,Zn)Al6(PO4)4(OH)8 · 4H2O |
| 8.DD.15 | 'Coeruleolactite' | |
| 8.DD.15 | Faustite | ZnAl6(PO4)4(OH)8 · 4H2O |
| 8.DD.15 | Planerite | Al6(PO4)2(PO3OH)2(OH)8 · 4H2O |
| 8.DD.15 | Chalcosiderite | CuFe3+6(PO4)4(OH)8 · 4H2O |
| 8.DD.15 | Turquoise | CuAl6(PO4)4(OH)8 · 4H2O |
| 8.DD.20 | Eosphorite | Mn2+Al(PO4)(OH)2 · H2O |
| 8.DD.20 | Ernstite | (Mn2+,Fe3+)Al(PO4)(OH,O)2 · H2O |
| 8.DD.20 | Lefontite | Fe2Al2Be(PO4)2(OH)6 |
| 8.DD.20 | Childrenite | Fe2+Al(PO4)(OH)2 · H2O |
| 8.DD.25 | Kobokoboite | Al6(PO4)4(OH)6 · 11H2O |
| 8.DD.30 | Smamite | Ca2Sb(OH)4[H(AsO4)2] · 6H2O |
| 8.DD.35 | 'Gutsevichite' | Al3(PO4)2(OH)3 · 8H2O |
| 8.DD.40 | 'Laubmannite (of Moore)' | (Fe3+,Fe2+,M)8+x(OH,H2O)9(H2O)2(PO4)5, M = Fe3+, Cu2+ or other metal cation, x ~ 0.1. |
Other Information
Thermal Behaviour:
Transformation to penberthycroftyite: 67-97°C, associated with 8% contraction of layer separation and 6Å relative sliding of the adjacent layers; T>100°C: formation of a "displaced-layer" phase, associated with further 8% layer contraction.
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 Bettertonite
mindat.org URL:
https://www.mindat.org/min-46516.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Bettertonite
Reference List:
Williams, P. A., Hatert, F., Pasero, M., Mills, S. J. (2015) New minerals and nomenclature modifications approved in 2014 and 2015. Newsletter No 23. Mineralogical Magazine, 79 (1) 51-58 doi:10.1180/minmag.2015.079.1.05
Grey, I.E., Kampf, A.R., Price, J.R., Macrae, C.M. (2015) Bettertonite, [Al6(AsO4)3(OH)9(H2O)5]·11H2O, a new mineral from the Penberthy Croft mine, St. Hilary, Cornwall, UK, with a structure based on polyoxometalate clusters. Mineralogical Magazine, 79 (7) 1849-1858 doi:10.1180/minmag.2015.079.7.16
Localities for Bettertonite
Showing 2 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.
UK | |
| |
| Williams et al. (2015) +1 other reference |
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Penberthy Croft Mine, St Hilary, Cornwall, England, UK