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⇱ Petermegawite: Mineral information, data and localities.

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Petermegawite

A valid IMA mineral species
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About PetermegawiteHide

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Formula:
Al6(Se4+O3)3[SiO3(OH)](OH)9 · 10H2O
Colour:
colorless
Lustre:
Vitreous
Hardness:
2 - 2½
Specific Gravity:
2.27
Crystal System:
Orthorhombic
Name:
Named after Dr Peter Megaw, of Tucson, Arizona, an exploration geologist who has worked and collected minerals all over Mexico for over 35 years, and who is the Mindat expert and reviewer for Mexican minerals. He has published extensively on Mexican mines and minerals, and also promotes appreciation for mineral recognition among exploration geologists as the basis for "visual geochemistry" in their projects. Recently he has also been engaged as an exploration geologist in Potosí Department, Bolivia, and he puts in lots of volunteer hours helping the Tucson Gem and Mineral Society organize the world's most important mineral show.
New structure type. Unique combination of elements (at the upload time). The first selenate (selenite) - silicate mineral to date. Third Al-Se mineral after alfredopetrovite and llantenesite.

A polyoxometallate in terms of its anion - [Al6(SiO3OH)O6(OH)9(H2O)6]6− - topologically identical to the arsenic-bearing ones in bettertonite and penberthycroftite.

The clusters comprise 6-membered rings of edge-sharing AlO6 octahedra and SiO3(OH) tetrahedra residing at centres of each ring. Three SeO3 triangular pyramids are outside the particular ring. The clusters are merged via hydrogen bonds to form heteropolyhedral layers || (001). The water molecules - not bonded to any non-hydrogen cations - are located between the layers.


Unique IdentifiersHide

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Mindat ID:
55696
Long-form identifier:
mindat:1:1:55696:7

IMA Classification of PetermegawiteHide

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Approved

Classification of PetermegawiteHide

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4.JJ.

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
J : Arsenites, antimonites, bismuthites, sulfites, selenites, tellurites; iodates
J : Selenites with additional anions, with H2O

Mineral SymbolsHide

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As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.

SymbolSourceReference for Standard
PmwIMA–CNMNCWarr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43

Physical Properties of PetermegawiteHide

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Vitreous
Transparency:
Transparent
Colour:
Colorless
Streak:
White
Hardness:
2 - 2½ on Mohs scale
Tenacity:
Brittle
Cleavage:
Perfect
{001}
Density:
2.27(5) g/cm3 (Measured)    2.32 g/cm3 (Calculated)

Optical Data of PetermegawiteHide

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Type:
Biaxial (+)
RI values:
nα = 1.545(5) nβ = 1.554(5) nγ = 1.567(5)
Max. Birefringence:
δ = 0.022
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.

Surface Relief:
Moderate

Chemistry of PetermegawiteHide

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Mindat Formula:
Al6(Se4+O3)3[SiO3(OH)](OH)9 · 10H2O
Element Weights:
Element% weight
O52.832 %
Se24.444 %
Al16.706 %
H3.120 %
Si2.898 %

Calculated from ideal end-member formula.

Crystallography of PetermegawiteHide

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Crystal System:
Orthorhombic
Class (H-M):
mm2 - Pyramidal
Space Group:
Cmc21
Cell Parameters:
a = 16.2392(2) Å, b = 10.9637(1) Å, c = 15.3367(2) Å
Ratio:
a:b:c = 1.481 : 1 : 1.399
Unit Cell V:
2,730.57 ų (Calculated from Unit Cell)
Z:
4

X-Ray Powder DiffractionHide

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Powder Diffraction Data:
d-spacingIntensity
7.824 Å(100)
7.642 Å(88)
5.839 Å(53)
5.580 Å(83)
5.514 Å(88)
4.860 Å(67)
4.496 Å(49)
3.017 Å(81)

Type Occurrence of PetermegawiteHide

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General Appearance of Type Material:
aggregates of bladed or tabular crystals
Place of Conservation of Type Material:
collections of (1) the University of Arizona Mineral Museum, 1040 E. 4th Street, Tucson, AZ 85721-0077, USA, catalogue no. 22711 (holotype), and (2) the RRUFF Project, deposition no. R210008 (cotype)
Geological Setting of Type Material:
Oxidation zone of a Se-rich deposit
Associated Minerals at Type Locality:

Other Language Names for PetermegawiteHide

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Common AssociatesHide

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Associations Based on Photo Data:
1 photo of Petermegawite associated with ChalcomeniteCuSeO3 · 2H2O

Related Minerals - Strunz-mindat GroupingHide

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4.JJ.XLarisaiteNa(H3O)(UO2)3(SeO3)O2 · 4H2OMon. m : Pm
4.JJ.BorzęckiitePb(UO2)3(SeO3)2O2 · 3H2OOrth. mm2
4.JJ.Amurselite(NH4)2(UO2)5(SeO3)3O2(OH)2(H2O) · 8H2OTric. 1 : P1
4.JJ.05MarthoziteCu2+(UO2)3(SeO3)2O2 · 8H2OOrth. mm2
4.JJ.10GuilleminiteBa(UO2)3(SeO3)2O2 · 3H2OOrth. mm2 : Pmn21
4.JJ.15PiretiteCa(UO2)3(SeO3)2(OH)4 · 4H2OOrth.
4.JJ.20DemesmaekeritePb2Cu5(UO2)2(SeO3)6(OH)6 · 2H2OTric. 1 : P1
4.JJ.25Haynesite(UO2)3(Se4+O3)2(OH)2 · 5H2OOrth.
4.JJ.30FavreauitePbBiCu6O4(SeO3)4(OH) · H2OTet. 4/m : P4/n

Other InformationHide

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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 PetermegawiteHide

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mindat.org URL:
https://www.mindat.org/min-55696.html
Please feel free to link to this page.

References for PetermegawiteHide

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Localities for PetermegawiteHide

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Showing 1 localities.

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

Locality ListHide

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👁 Image
- This locality has map coordinates listed. 👁 Image
- This locality has estimated coordinates. ⓘ - Click for references and further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. 👁 Image
- Good crystals or important locality for species. 👁 Image
- 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 (e.g. from pseudomorphs).

All localities listed without proper references should be considered as questionable.
Bolivia (TL)
  • Potosí
    • Antonio Quijarro Province
      • Porco Municipality
Miyawaki et al. (2021)
Quick NavTopAbout PetermegawiteUnique IdentifiersIMA Classification Classification Mineral SymbolsPhysical Properties Optical Data Chemistry Crystallography X-Ray Powder DiffractionType Occurrence Other LanguagesCommon AssociatesStrunz-MindatOther InformationInternet Links References Localities Locality List
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