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Arnhemite

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Formula:
(K,Na)
 
4
Mg
 
2
(P
 
2
O
 
7
)
 
2
 · 5H
 
2
O
System:HexagonalColour:White
Lustre:Pearly
Name:Named after its locality.


A hydrated pyrophospate originated from hydration of slag forme by bat guano combustion in Arnhem Cave, Namibia, about 2000 years ago. Cause of combustion unknown.

Originally reported from Arnhem Cave, Windhoek District, Khomas Region, Namibia.

Classification of Arnhemite

IMA status:Published without Approval
Nickel-Strunz 10th (pending) edition ID:8.FC.20

8 : PHOSPHATES, ARSENATES, VANADATES
F : Polyphosphates, Polyarsenates, [4]-Polyvanadates
C : Polyphosphates, etc., with H2O only
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Physical Properties of Arnhemite

Lustre:Pearly
Colour:White

Crystallography of Arnhemite

Crystal System:Hexagonal

Optical Data of Arnhemite

Type:Uniaxial (-)
RI values: nω = 1.516 nε = 1.503
Maximum Birefringence:δ = 0.013

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Low

Chemical Properties of Arnhemite

Formula:
(K,Na)
 
4
Mg
 
2
(P
 
2
O
 
7
)
 
2
 · 5H
 
2
O
Essential elements:H, K, Mg, O, P
All elements listed in formula:H, K, Mg, Na, O, P

Relationship of Arnhemite to other Species

Related Minerals - Nickel-Strunz Grouping):

- +
8.FC.05Fianelite
Mn
2+
2
((V,As)
 
2
O
 
7
) · 2H
 
2
O
8.FC.10Canaphite
Na
 
2
Ca(P
 
2
O
 
7
) · 4H
 
2
O
8.FC.15Pintadoite
Ca
 
2
(V
 
2
O
 
7
) · 9H
 
2
O
8.FC.25Wooldridgeite
Na
 
2
CaCu
2+
2
(P
 
2
O
 
7
)
 
2
 · 10H
 
2
O
8.FC.30Kanonerovite
Na
 
3
Mn
2+
 
(P
 
3
O
 
10
) · 12H
 
2
O

Other Names for Arnhemite

Other Languages:
German:Arnhemit
Spanish:Arnhemita

Other Information

Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Arnhemite

Reference List:

- +
Martini, J. E. (1994): Two new minerals originated from bat guano combustion in Arnhem Cave, Namibia. South African Speleological Assoc. Bull. 33, 66-69. [Abstract in Am. Mineral. 84, 193]

Internet Links for Arnhemite

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    • Localities for Arnhemite

    The 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.
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    (TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
    Namibia
     
    • Khomas Region
      • Windhoek District
    		[South African Speleological Assoc.(1994) 33, 66-69; AmMin 84:193]
    Saudi Arabia
     
    • Mintaqah Makkah
    		Saudi Geological Survey Open-File Report SGS-OF-2004-12, 68 p.
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