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Vitreous, Silky, Pearly
Specific Gravity:
2.02 (Calculated)
Crystal System:
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.
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).

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Classification of BettertoniteHide

Approval Year:

Pronounciation of BettertoniteHide

PlayRecorded byCountry
Jolyon & Katya RalphUnited Kingdom

Physical Properties of BettertoniteHide

Vitreous, Silky, Pearly
Vitreous to pearly, somewhat silky lustre
2.02 g/cm3 (Calculated)

Optical Data of BettertoniteHide

Biaxial (+)
RI values:
nα = 1.511(1) nβ = 1.517(1) nγ = 1.523(1)
Max Birefringence:
δ = 0.012
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:

Chemical Properties of BettertoniteHide

IMA Formula:
Al6(AsO4)3(OH)9(H2O)5 · 11H2O

Crystallography of BettertoniteHide

Crystal System:
Class (H-M):
2/m - Prismatic
Space Group:
Cell Parameters:
a = 7.773(2) Å, b = 26.991(5) Å, c = 15.867(3) Å
β = 94.22(3)°
a:b:c = 0.288 : 1 : 0.588
Unit Cell V:
3,319.89 ų (Calculated from Unit Cell)
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 DiffractionHide

Powder Diffraction Data:
From Type Description.

Type Occurrence of BettertoniteHide

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:

Synonyms of BettertoniteHide

Other InformationHide

Thermal Behaviour:
transformation to penberthycroftyite: 67-97oC, associated with 8% contraction of layer separation and 6Å relative sliding of the adjacent layers; T>100oC: formation of a "displaced-layer" phase, associated with further 8% layer cont
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for BettertoniteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Grey, I.E., Kampf, A.R., Price, J.R. and MacRae, C.M. (2015) Bettertonite, IMA 2014-074. CNMNC Newsletter No. 23, February 2015, page 55; Mineralogical Magazine, 79, 51-58.
Grey, I.E., Kampf, A.R., Price, J.R. and 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 49, 1849-1858.
Grey, I.E., Brand, H.E.A., Betterton, J. (2016): Dehydration phase transitions in new aluminium arsenate minerals from the Penberthy Croft mine, Cornwall. Mineralogical Magazine: 80: 1205-1217

Internet Links for BettertoniteHide

Localities for BettertoniteHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for 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). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (eg from pseudomorphs.)

All localities listed without proper references should be considered as questionable.
  • England
    • Cornwall
      • St Hilary
Grey, I.E., Kampf, A.R., Price, J.R., MacRae, C.M. (2015) Bettertonite, IMA 2014-074. CNMNC Newsletter No. 23, February 2015, page 55. Williams, P.A., Hatert, F., Pasero, M., Mills, S.J. (2015) New minerals and nomenclature modifications approved in 2014 and 2015. Mineralogical Magazine, 79:1, 51-58. [[1]] 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.
Mineral and/or Locality  
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