Arnhemite
Valid as an unnamed mineral
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Formula:
(K,Na)4Mg2(P2O7)2 · 5H2O
Colour:
White
Lustre:
Pearly
Crystal System:
Hexagonal
Name:
Named after its locality.
A hydrated pyrophospate originated from hydration of slag formed by bat guano combustion in Arnhem Cave, Namibia, about 2000 years ago. Cause of combustion unknown.
See also pyrocoproite and pyrophosphite; UM1991-10-PO:BaCaHMgSr; and approved pyrophosphate minerals: canaphite, anastasenkoite, and wooldridgeite.
Originally reported from Arnhem Cave, Windhoek District, Khomas Region, Namibia.
See also pyrocoproite and pyrophosphite; UM1991-10-PO:BaCaHMgSr; and approved pyrophosphate minerals: canaphite, anastasenkoite, and wooldridgeite.
Originally reported from Arnhem Cave, Windhoek District, Khomas Region, Namibia.
Unique Identifiers
Mindat ID:
6806
Long-form identifier:
mindat:1:1:6806:8
IMA Classification of Arnhemite
IMA status notes:
Unnamed (probably valid)
Approval history:
Unnamed, but probably valid.
Classification of Arnhemite
8.FC.20
8 : PHOSPHATES, ARSENATES, VANADATES
F : Polyphosphates, Polyarsenates, [4]-Polyvanadates
C : Polyphosphates, etc., with H2O only
8 : PHOSPHATES, ARSENATES, VANADATES
F : Polyphosphates, Polyarsenates, [4]-Polyvanadates
C : Polyphosphates, etc., with H2O only
Physical Properties of Arnhemite
Pearly
Colour:
White
Optical Data of Arnhemite
Type:
Uniaxial (-)
RI values:
nω = 1.516 nε = 1.503
Max. Birefringence:
δ = 0.013
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 uniaxial interference figure - the conoscopic
(convergent-light, Bertrand-lens-in) view, for a grain cut with the optic axis
centred and vertical. The coloured rings are isochromatics, computed with the
same physics as the Michel-Lévy bar above; the dark cross is the isogyre.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
Chemistry of Arnhemite
Mindat Formula:
(K,Na)4Mg2(P2O7)2 · 5H2O
Element Weights:
Crystallography of Arnhemite
Crystal System:
Hexagonal
Other Language Names for Arnhemite
Related Minerals - Strunz-mindat Grouping
| 8.FC. | Donowensite | Ca(H2O)3Fe3+2(V2O7)2 |
| 8.FC.X | Hylbrownite | Na3Mg(P3O10) · 12H2O |
| 8.FC.05 | Fianelite | Mn2+2((V,As)2O7) · 2H2O |
| 8.FC.05 | Rüdlingerite | Mn2+2V5+As5+O7 · 2H2O |
| 8.FC.10 | Canaphite | Na2Ca(P2O7) · 4H2O |
| 8.FC.15 | Pintadoite | Ca2(V2O7) · 9H2O |
| 8.FC.25 | Wooldridgeite | Na2CaCu2+2(P2O7)2 · 10H2O |
| 8.FC.30 | Kanonerovite | Na3Mn2+(P3O10) · 12H2O |
| 8.FC.35 | Mesaite | CaMn2+5(V2O7)3 · 12H2O |
Radioactivity
Other Information
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 Arnhemite
mindat.org URL:
https://www.mindat.org/min-6806.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Arnhemite
Localities for Arnhemite
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.
Namibia | |
| Martini (1994) +1 other reference |
Saudi Arabia | |
| Saudi Geological Survey Open-File ... +1 other reference |
