Selwynite Mineral Data

Selwynite Mineral Data +

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General Selwynite Information

Chemical Formula:

NaK(Be,Al)Zr2(PO4)4·2(H2O)

Composition:

Molecular Weight = 673.96 gm

Potassium 5.80 % K 6.99 % K₂O

Sodium 3.41 % Na 4.60 % Na₂O

Zirconium 27.07 % Zr 36.57 % ZrO₂

Beryllium 1.00 % Be 2.78 % BeO

Aluminum 1.00 % Al 1.89 % Al₂O₃

Phosphorus 18.38 % P 42.12 % P₂O₅

Hydrogen 0.60 % H 5.35 % H₂O

Oxygen 42.73 % O

______ ______

100.00 % 100.30 % = TOTAL OXIDE

Empirical Formula:

NaKBe_0.75Al_0.25Zr₂(PO₄)₄·2(H₂O)

Environment:

In pegmatitic cavities.

IMA Status:

Approved IMA 1995

Locality:

A granite quarry near Wycheproof, NW Victoria, Australia. Link to MinDat.org Location Data.

Name Origin:

For A. R. C. Selwyn (1824-1902), founding director of the Geological Survey of Victoria, Australia.

Synonym:

IMA1993-037

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Selwynite Crystallography

Axial Ratios:

a:c = 1:2.60913

Cell Dimensions:

a = 6.57, c = 17.142, Z = 2; V = 739.93 Den(Calc)= 3.02

Crystal System:

Tetragonal - Ditetragonal DipyramidalH-M Symbol (4/m 2/m 2/m) Space Group: I 4₁/amd

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

By Intensity(I/I_o): 6.161(1), 3.286(0.5), 3.039(0.3),

Physical Properties of Selwynite

Cleavage:

None

Color:

Deep purplish blue.

Density:

2.94

Diaphaniety:

Transparent

Fracture:

Sub Conchoidal - Fractures developed in brittle materials characterized by semi-curving surfaces.

Habit:

Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite)

Hardness:

4 - Fluorite

Luminescence:

Non-fluorescent.

Luster:

Vitreous (Glassy)

Streak:

pale lavender

Optical Properties of Selwynite

Dichroism (e):

bluish lavender.

Dichroism (w):

pale bluish lavender.

Gladstone-Dale:

CI meas= -0.043 (Good) - where the CI = (1-KPDmeas/KC)
CI calc= -0.015 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2086,KPDmeas= 0.2143,KC= 0.2054

Optical Data:

Uniaxial (+), w=1.624, e=1.636, bire=0.0120.

Calculated Properties of Selwynite

Electron Density:

r_electron=2.91 gm/cc
note: r_Selwynite=3.02 gm/cc.

Fermion Index

Fermion Index = 0.04061
Boson Index = 0.95939

Photoelectric:

PE_Selwynite= 37.76 barns/electron
U=PE_Selwynite x r_electron= 109.72 barns/cc.

Radioactivity:

GRapi = 80.55 (Gamma Ray American Petroleum Institute Units)

Estimated Radioactivity from Selwynite - barely detectable

Selwynite Classification

Dana Class:

40.5.4.3 (40)Hydrated Phosphates, etc

(40.5)with miscellaneous formulae

(40.5.4)Dana Group

40.5.4.1 Gainesite Na2Zr2Be(PO4)4·1-2(H2O) I 4₁/amd 4/m 2/m 2/m

40.5.4.2 Mccrillisite NaCs(Be,Li)Zr2(PO4)4·1-2(H2O) I 4₁/amd 4/m 2/m 2/m

40.5.4.3 Selwynite NaK(Be,Al)Zr2(PO4)4·2(H2O) I 4₁/amd 4/m 2/m 2/m

Strunz Class:

VII/C.02-25 VII - Phosphates, Arsenates and Vanadates

VII/C - Water-bearing phosphates without unfamiliar anions. cations of medium and small size: Be and Mn, Fe, Cu, Zn, Mg

VII/C.02 - Faheyite - Gainesite-(NaCs) series

VII/C.02-10 Faheyite (Mn,Mg)Fe2Be2(PO4)4·6(H2O) P 6₂22 6 2 2

VII/C.02-20 Melilite (Ca,Na)2(Al,Mg,Fe)(Si,Al)2O7 P 42₁m 4 2m

VII/C.02-25 Selwynite NaK(Be,Al)Zr2(PO4)4·2(H2O) I 4₁/amd 4/m 2/m 2/m

VII/C.02-35 Gainesite Na2Zr2Be(PO4)4·1-2(H2O) I 4₁/amd 4/m 2/m 2/m

VII/C.02-40 Mccrillisite NaCs(Be,Li)Zr2(PO4)4·1-2(H2O) I 4₁/amd 4/m 2/m 2/m

Other Selwynite Information

References:

NAME( MinRec) PHYS. PROP.(Am.Min.,Vol.80,p1075,1995) OPTIC PROP.(MinRec)

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Selwynite

NaK(Be,Al)Zr2(PO4)4·2(H2O)
Dana No: 40.5.4.3 Strunz No: VII/C.02-25
Locality:

Notes: