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Arnhemite

Formula:
(K,Na)
 
4
Mg
 
2
(P
 
2
O
 
7
)·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
)·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
5+
 
(V
5+
 
,As
5+
 
)O
 
7
·2H
 
2
O
8.FC.10Canaphite
CaNa
 
2
[HPO
 
4
]
 
2
 · 3H
 
2
O
8.FC.15Pintadoite
Ca
 
2
V
 
2
O
 
7
·9H
 
2
O
8.FC.25Wooldridgeite
CaNa
 
2
Cu
2+
2
[P
 
2
O
 
7
]
 
2
 · 10H
 
2
O
8.FC.30Kanonerovite
MnNa
 
3
P
 
3
O
 
10
 * 12 H
 
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]

Articles/Blogs about Arnhemite

Internet Links for Arnhemite

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    Localities for Arnhemite

    (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]
    Mineral and/or Locality
    Google
     
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