Johnwalkite Mineral Data

Johnwalkite Mineral Data +

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General Johnwalkite Information

Chemical Formula:

K(Mn++,Fe+++,Fe++)2(Nb,Ta)(PO4)2O2((H2O),OH)2

Composition:

Molecular Weight = 480.93 gm

Potassium 7.32 % K 8.81 % K₂O

Magnesium 0.51 % Mg 0.84 % MgO

Tantalum 3.76 % Ta 4.59 % Ta₂O₅

Manganese 11.42 % Mn 14.75 % MnO

Niobium 15.45 % Nb 22.11 % Nb₂O₅

Iron 9.29 % Fe 13.28 % Fe₂O₃

Phosphorus 12.24 % P 28.04 % P₂O₅

Hydrogen 0.75 % H 6.74 % H₂O

Oxygen 39.26 % O

______ ______

100.00 % 99.17 % = TOTAL OXIDE

Empirical Formula:

K_0.9Mn²⁺Fe³⁺_0.7Mg_0.1Nb_0.8Ta_0.1Fe³⁺_0.1O₂(PO₄)_1.9(H₂O)_1.4(OH)_0.8

Environment:

Secondary mineral derived from the dissolution of triphylite-lithiophilite and columbite-tantalite in a complex granite pegmatite.

IMA Status:

Approved IMA 1986

Locality:

Expectation pegmatite at the Champion mine, about 2.5 km southeast of Keystone, Pennington County, South Dakota, USA. Link to MinDat.org Location Data.

Name Origin:

Named for Richard JOHNson (1936-1998) and Frank WALKup (1943-1993), mineral preparators, National Museum of Natural History, Washington, D. C., USA.

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Johnwalkite Crystallography

Axial Ratios:

a:b:c =0.7498:1:0.6487

Cell Dimensions:

a = 7.516, b = 10.023, c = 6.502, Z = 2; V = 489.81 Den(Calc)= 3.26

Crystal System:

Orthorhombic - PyramidalH-M Symbol (mm2) Space Group: Pb21m

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

By Intensity(I/I_o): 6.01(1), 3.005(0.8), 3.054(0.7),

Physical Properties of Johnwalkite

Cleavage:

[001] Good, [100] Good

Color:

Dark reddish brown, Reddish brown.

Density:

3.4

Diaphaniety:

Transparent to Translucent

Fracture:

Brittle - Generally displayed by glasses and most non-metallic minerals.

Habit:

Aggregates - Made of numerous individual crystals or clusters.

Habit:

Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).

Habit:

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

Hardness:

4 - Fluorite

Luster:

Vitreous (Glassy)

Streak:

greenish yellow

Optical Properties of Johnwalkite

Gladstone-Dale:

CI meas= -0.001 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= -0.044 (Good) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2404,KPDmeas= 0.2305,KC= 0.2303

Optical Data:

Biaxial (+), a=1.748, b=1.763, g=1.84, bire=0.0920, 2V(Calc)=50, 2V(Meas)=53.

Pleochroism (x):

blue green.

Pleochroism (y):

yellow or pale brown.

Pleochroism (z):

brown.

Calculated Properties of Johnwalkite

Electron Density:

r_electron=3.26 gm/cc
note: r_Johnwalkite=3.40 gm/cc.

Fermion Index

Fermion Index = 0.00267
Boson Index = 0.99733

Photoelectric:

PE_Johnwalkite= 70.30 barns/electron
U=PE_Johnwalkite x r_electron= 229.33 barns/cc.

Radioactivity:

GRapi = 101.29 (Gamma Ray American Petroleum Institute Units)

Estimated Radioactivity from Johnwalkite - barely detectable

Johnwalkite Classification

Dana Class:

42.7.11.2 (42)Hydrated Phosphates, etc., Containing Hydroxyl or Halogen

(42.7)where (AB)5 (XO4)3 Zq · x(H2O)

(42.7.11)Dana Group

42.7.11.1 Olmsteadite KFe2(Nb,Ta)(PO4)2O2·2(H2O) Pb21m mm2

42.7.11.2 Johnwalkite K(Mn,Fe,Fe)2(Nb,Ta)(PO4)2O2((H2O),OH)2 Pb21m mm2

Strunz Class:

VII/D.39-20 VII - Phosphates, Arsenates and Vanadates

VII/D - Water-bearing phosphates with unfamiliar anions, cations of very big and medium size: Al, Mg and Ca, Na, K

VII/D.39 - Olmsteadite - Johnwalkite series

VII/D.39-10 Olmsteadite KFe2(Nb,Ta)(PO4)2O2·2(H2O) Pb21m mm2

VII/D.39-20 Johnwalkite K(Mn,Fe,Fe)2(Nb,Ta)(PO4)2O2((H2O),OH)2 Pb21m mm2

Other Johnwalkite Information

References:

NAME( AntBidBlaNic4) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(AntBidBlaNic4)

See Also:

Links to other databases for Johnwalkite :
1 -Am. Min. Crystal Structure Database 2 -Athena 3 - EUROmin Project 4 -Google Images 5 -Google Scholar 6 -MinDAT 7 -MinMax(Deutsch) 8 -MinMax(English) 9 -Mineralienatlas (Deutsch) 10 -QUT Mineral Atlas 11 - WWW-MINCRYST 12 -École des Mines de Paris

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Print or Cut-and-Paste your Johnwalkite Specimen Label here :

Johnwalkite

K(Mn++,Fe+++,Fe++)2(Nb,Ta)(PO4)2O2((H2O),OH)2
Dana No: 42.7.11.2 Strunz No: VII/D.39-20
Locality:

Notes: