Penberthycroftite
A valid IMA mineral species
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About Penberthycroftite
Daw's Shaft, Penberthy Croft Mine (viewed from N side)
Penberthy Croft Mine, St Hilary, Cornwall, England, UK
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.
Type Locality:
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.
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.
Unique Identifiers
Mindat ID:
46688
Long-form identifier:
mindat:1:1:46688:6
IMA Classification of Penberthycroftite
Classification of Penberthycroftite
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 |
|---|---|---|
| Pbc | 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 Penberthycroftite
Pronunciation:
| Play | Recorded by | Country |
|---|---|---|
| Jolyon Ralph | United Kingdom |
Physical Properties of Penberthycroftite
Vitreous, Pearly
Transparency:
Translucent
Comment:
Crusts have dull and nearly waxy lustre.
Colour:
White
Streak:
White
Tenacity:
Flexible
Cleavage:
Perfect
Basal cleavage on {010}
Basal cleavage on {010}
Density:
2.18 g/cm3 (Calculated)
Chemistry of Penberthycroftite
Mindat Formula:
[Al6(AsO4)3(OH)9(H2O)5] · 8H2O
Element Weights:
Elements listed:
Common Impurities:
S,(Fe)
Crystallography of Penberthycroftite
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)°
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 Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 13.264 Å | (46) |
| 12.402 Å | (16) |
| 9.732 Å | (100) |
| 7.420 Å | (28) |
| 5.670 Å | (8) |
| 5.423 Å | (6) |
| 3.598 Å | (6) |
| 3.562 Å | (6) |
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 Penberthycroftite
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 Penberthycroftite
Other Language Names for Penberthycroftite
Dutch:Penberthycroftiet
German:Penberthycroftit
Common Associates
Associations Based on Photo Data:
| 1 photo of Penberthycroftite associated with Pharmacosiderite | KFe3+4(AsO4)3(OH)4 · 6-7H2O |
Related Minerals - Strunz-mindat Grouping
| 8.DD. | Bettertonite | [Al6(AsO4)3(OH)9(H2O)5] · 11H2O |
| 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. |
Fluorescence of Penberthycroftite
none
Other Information
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.
Internet Links for Penberthycroftite
mindat.org URL:
https://www.mindat.org/min-46688.html
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References for Penberthycroftite
Reference List:
Hålenius, U., Hatert, F., Pasero, M., Mills, S. J. (2015) New minerals and nomenclature modifications approved in 2015, CNMNC Newsletter 26. Mineralogical Magazine, 79 (4) 941-947 doi:10.1180/minmag.2015.079.4.05
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 doi:10.1180/minmag.2016.080.069
Localities for Penberthycroftite
Showing 1 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 (TL) | |
| Hålenius et al. (2015) +1 other reference |
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Penberthy Croft Mine, St Hilary, Cornwall, England, UK