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Penberthycroftite

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Daw's Shaft, Penberthy Croft Mine (viewed from N side)

Penberthy Croft Mine, St Hilary, Cornwall, England, UK
Formula:
[Al6(AsO4)3(OH)9(H2O)5]·8H2O
Colour:
White
Lustre:
Vitreous, Pearly
Specific Gravity:
2.18 (Calculated)
Crystal System:
Monoclinic
Name:
The mineral is named for the location where the mineral was found, Penberthy Croft mine.
Closely related to bettertonite, which is a higher hydrate. Also chemically similar to liskeardite, bulachite, and hydroniumpharmacoalumite; and to mansfieldite.

The structure is heteropolyhedral layered one, with undulating layering || {010}. In the structure there are channels along [100] holding water molecules. The layers are identical to that in bettertonite, but are mutually displaced along [001] and [010] resulting in the interlayer volume decrease, by ca. 10%, when compared to bettertonite.


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Classification of PenberthycroftiteHide

Approved
Approval Year:
2015
First Published:
2016

Pronounciation of PenberthycroftiteHide

Pronounciation:
PlayRecorded byCountry
Jolyon & Katya RalphUnited Kingdom

Physical Properties of PenberthycroftiteHide

Vitreous, Pearly
Transparency:
Translucent
Comment:
Crusts have dull and nearly waxy lustre.
Colour:
White
Streak:
White
Tenacity:
Flexible
Cleavage:
Perfect
Basal cleavage on {010}
Density:
2.18 g/cm3 (Calculated)

Chemical Properties of PenberthycroftiteHide

Formula:
[Al6(AsO4)3(OH)9(H2O)5]·8H2O
IMA Formula:
[Al6(AsO4)3(OH)9(H2O)5] · 8H2O
Common Impurities:
S,(Fe)

Crystallography of PenberthycroftiteHide

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/b
Setting:
P21/c
Cell Parameters:
a = 7.753(2) Å, b = 24.679(5) Å, c = 15.679(3) Å
β = 94.19(3)°
Ratio:
a:b:c = 0.314 : 1 : 0.635
Unit Cell V:
2,991.94 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Tufts and sprays of ultrathin (sub-micrometre) rectangular or bladelike laths, with lateral dimensions generally less than 20µm.

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
13.264(46)
12.402(16)
9.732(100)
7.420(28)
5.670(8)
5.423(6)
3.598(6)
3.562(6)

Type Occurrence of PenberthycroftiteHide

General Appearance of Type Material:
Dense lath-like crystal aggregates within a matrix of quartz, chamosite and arsenopyrite.
Place of Conservation of Type Material:
Co-type material is deposited in the mineralogical collections of the Natural History Museum, London, Registration number BM.2015.3 and the Museum Victoria, Australia, registration number M53452
Geological Setting of Type Material:
The arsenate mineral assemblage at Penberthy Croft is interpreted as having formed from prolonged oxidation of various sulphides in the upper parts of lodes and veins within the mine and on dump material.
Associated Minerals at Type Locality:

Synonyms of PenberthycroftiteHide

Fluorescence of PenberthycroftiteHide

Other InformationHide

Thermal Behaviour:
Two endotherms corresponding to water evolution were recorded at 94 and 180°C, and an endotherm due to SO3 evolution occurred at 481°C; will from from bettertonite at 67-97oC, the process being associated with 8% contraction of laye
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 PenberthycroftiteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Grey, I.E., Betterton, J., Kampf, A.R., Price, J.R. and MacRae, C.M. (2015) Penberthycroftite, IMA 2015-025. CNMNC Newsletter No. 26, August 2015, page 943; Mineralogical Magazine: 79: 941-947.
Grey, I.E., Betterton, J., Kampf, A.R., Macrae, C.M., Shanks, F.L., Price, J.R. (2016) Penberthycroftite, [Al6(AsO4)3(OH)9(H2O)5]·8H2O, a second new hydrated aluminium arsenate mineral from the Penberthy Croft mine, St. Hilary, Cornwall. Mineralogical Magazine: 80: 1149-1160.
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 PenberthycroftiteHide

Localities for PenberthycroftiteHide

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.
UK (TL)
 
  • England
    • Cornwall
      • St Hilary
Grey, I.E., Betterton, J., Kampf, A.R., Price, J.R. and MacRae, C.M. (2015) Penberthycroftite, IMA 2015-025. CNMNC Newsletter No. 26, August 2015, page 943. Mineralogical Magazine, 79, 941-947. Grey, I.E., Betterton, J., Kampf, A.R., Macrae, C.M., Shanks, F.L., Price, J.R. (2016) Penberthycroftite, [Al₆(AsO₄)₃(OH)₉ (H₂O)₅ ]·8H₂O, a second new hydrated aluminium arsenate mineral from the Penberthy Croft mine, St. Hilary, Cornwall, UK. Mineralogical Magazine, 80:7, 1149-1160.
Mineral and/or Locality  
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