Johnwalkite Mineral Data

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.

Name Pronunciation:

Johnwalkite + Pronunciation

Johnwalkite Image

Images:

Johnwalkite

Comments: Fragment of translucent johnwalkite.
Location: Champion Mine, Keystone District, Pennington Co., South Dakota, USA. Scale: Crystal length 1 mm.
© Jeff Weissman / Photographic Guide to Mineral Species

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 - Pyramidal H-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

Diaphaneity:

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
Ncalc = 1.75 - 1.78

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:

Bulk Density (Electron Density)=3.26 gm/cc
note: Specific Gravity of Johnwalkite =3.40 gm/cc.

Fermion Index:

Fermion Index = 0.0026776959
Boson Index = 0.9973223041

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)
Concentration of Johnwalkite per GRapi unit = 0.99 (%)

Estimated Radioactivity from Johnwalkite - barely detectable

Johnwalkite Classification

Dana Class:

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

(42.07)where (AB)5 (XO4)3 Zq ï¿½ x(H2O)

(42.07.11)Olmsteadite Group

42.07.11.01 Olmsteadite KFe2(Nb,Ta)(PO4)2O2•2(H2O) Pb21m mm2

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

Strunz Class:

08.DJ.05 08 - PHOSPHATES, ARSENATES, VANADATES

08.D - Phosphates, etc

08.DJ -With large and medium-sized cations, (OH, etc.):RO4 = 1:l

08.DJ.05 Johnwalkite K(Mn,Fe,Fe)2(Nb,Ta)(PO4)2O2((H2O),OH)2 Pb21m mm2

08.DJ.05 Olmsteadite KFe2(Nb,Ta)(PO4)2O2•2(H2O) 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 - Ecole des Mines de Paris
5 - GeoScienceWorld
6 - Google Images
7 - Google Scholar
8 - Handbook of Mineralogy (MinSocAm)
9 - MinDAT
10 - Mineralienatlas (Deutsch)
11 - Online Mineral Museum
12 - QUT Mineral Atlas
13 - Ruff.Info
14 - WWW-MINCRYST

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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: 42.07.11.02 Strunz No: 08.DJ.05
Locality:

Notes:

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