Arnhemite Mineral Data

General Arnhemite Information

Chemical Formula:

(K,Na)2Mg2(P2O7)•5(H2O)

Composition:

Molecular Weight = 620.94 gm

Potassium 17.50 % K 21.09 % K₂O

Sodium 3.37 % Na 4.54 % Na₂O

Calcium 0.97 % Ca 1.35 % CaO

Magnesium 6.89 % Mg 11.42 % MgO

Manganese 0.18 % Mn 0.23 % MnO

Zinc 0.11 % Zn 0.13 % ZnO

Iron 0.27 % Fe 0.35 % FeO

Phosphorus 20.10 % P 46.06 % P₂O₅

Hydrogen 1.66 % H 14.83 % H₂O

Oxygen 48.96 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

K_2.78Na_0.91Mg_1.76Ca_0.15Fe²⁺_0.03Mn²⁺_0.02Zn_0.01P_4.03O_13.89ï¿½5.11(H₂O)

Environment:

Occurs as flakes that form aggregates making up the principal component of a thin layer of white, friable slag in the profile of cave-floor soil.

IMA Status:

Not Approved IMA

Locality:

Arnhem Cave, Namibia. Link to MinDat.org Location Data.

Name Origin:

Named after it's locality.

Arnhemite Crystallography

Axial Ratios:

a:c = 1:1.51446

Cell Dimensions:

a = 11.06, c = 16.75, Z = 4; V = 1,774.42 Den(Calc)= 2.32

Crystal System:

Hexagonal Space Group: Unk

$Help on X Ray Diffraction:$ X Ray Diffraction:

By Intensity(I/I_o): 16.7(1)(001 ), 2.761(0.25)(220 ), 8.33(0.15)(011 ),2.3(0.1)(224,042), 2.216(0.05)(126 ), 4.616(0.05)(112 ), 3.184(0.05)(030 ),

Physical Properties of Arnhemite

Cleavage:

{001} Perfect

Color:

White.

Density:

2.33 - 2.35, Average = 2.34

Diaphaneity:

Transparent

Fracture:

Friable - The crumbly disintegration of earthy materials or highly fractured minerals.

Luster:

Pearly

Streak:

white

Optical Properties of Arnhemite

Gladstone-Dale:

CI meas= -0.029 (Excellent) - where the CI = (1-KPDmeas/KC)
CI calc= -0.038 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2196,KPDmeas= 0.2177,KC= 0.2117
Ncalc = 1.49 - 1.5

Optical Data:

Uniaxial (-), e=1.503, w=1.516, bire=0.0130.

Calculated Properties of Arnhemite

Electron Density:

Bulk Density (Electron Density)=2.35 gm/cc
note: Specific Gravity of Arnhemite =2.34 gm/cc.

Fermion Index:

Fermion Index = 0.0072609178
Boson Index = 0.9927390822

Photoelectric:

PE_Arnhemite= 3.22 barns/electron
U=PE_Arnhemite x r_electron= 7.54 barns/cc.

Radioactivity:

GRapi = 253.16 (Gamma Ray American Petroleum Institute Units)
Concentration of Arnhemite per GRapi unit = 0.40 (%)

Estimated Radioactivity from Arnhemite - barely detectable

Arnhemite Classification

Dana Class:

37.00.00.00 (37)Phosphate Minerals

(37.00)Without Dana Classification Numbers

(37.00.00)Phosphate, Thermocaca Series

37.00.00.00 Arnhemite* (K,Na)2Mg2(P2O7)•5(H2O) Unk Hex

37.00.00.00 Arsenowaylandite* BiAl3(AsO4)2(OH)6 R 3m 3 2/m

37.00.00.00 Auroantimonate* AuSbO3 Ortho ? Ortho

37.00.00.00 Barium-zinc-alumopharmacosiderite* (Ba,K)0.5(Zn,Cu)0.5(Al,Fe)4(AsO4)3•5(H2O) I 42m 4 2m

37.00.00.00 Chernovite-(Ce)* (Ce,Y)(AsO4) I 4₁/amd 4/m 2/m 2/m

37.00.00.00 Churchite-(Dy)* (Dy,Sm,Gd,Nd)(PO4)•2(H2O) Mono

37.00.00.00 Gengenbachite KFe3(H2PO4)2(HPO4)4•6H2OorKFe3H8(PO4)6•6H2O P 6₃mc 6mm

37.00.00.00 IMA2008-063 Pb[Zn0.25,[]0.75]Fe3H(AsO4)2(OH)6 C 2/c 2/m

37.00.00.00 IMA2009-005 (Y,Ca,REE)5[(Si,P)O4]3F P 6₃/m 6/m 2/m 2/m

37.00.00.00 IMA2009-016 Cu4H(AsO4)2(OH)3•H2O P1 1

37.00.00.00 Kerstenite? PbSeO4(?) P nma 2/m 2/m 2/m

37.00.00.00 Krasnoselskite* CoWO4 P 2/c 2/m

37.00.00.00 Laubmannite? Fe3Fe6(PO4)4(OH)12 Unk Ortho

37.00.00.00 Oxiberaunite* (Fe,Mn)Fe5(PO4)4O(OH)4•6(H2O) Mono

37.00.00.00 Parwanite (Na,K)(Mg,Ca)4Al8(PO4)8(CO3)(OH)7•30H2O P 2, Pm, P 2/m, P 2₁, Mono

37.00.00.00 Pyrocoproite* (Mg(K,Na))2P2O7 Unk Mono

37.00.00.00 Pyrophosphite* K2CaP2O7 P 2₁/n 2/m

37.00.00.00 Zinclavendulan? NaCa(Zn,Cu)5(AsO4)4Cl•4-5(H2O) Unk Ortho

Strunz Class:

08.FC.20 08 - PHOSPHATES, ARSENATES, VANADATES

08.F - Polyphosphates, Polyarsenates, [4]-Polyvanadates

08.FC -Polyphosphates, etc., with H2O only

08.FC.20 Arnhemite* (K,Na)2Mg2(P2O7)•5(H2O) Unk Hex

Other Arnhemite Information

References:

NAME( AmMin, v84:193) PHYS. PROP.(Am.Min.,Vol.84,p193,1999) OPTIC PROP.(AmMin, v84:193)

See Also:

Links to other databases for Arnhemite :
1 - Am. Min. Crystal Structure Database
2 - Athena
3 - GeoScienceWorld
4 - Google Images
5 - Google Scholar
6 - MinDAT
7 - Mineralienatlas (Deutsch)
8 - Online Mineral Museum
9 - QUT Mineral Atlas
10 - Ruff.Info

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Arnhemite

(K,Na)2Mg2(P2O7)•5(H2O)
Dana No: 37.00.00.00 Strunz No: 08.FC.20
Locality:

Notes:

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