Johnwalkite
A valid IMA mineral species
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About Johnwalkite
Formula:
K(Mn2+,Fe2+,Fe3+)2(Nb5+,Ta5+)(PO4)2O2 · 2(H2O,OH)
Colour:
Very dark reddish brown
Lustre:
Vitreous
Hardness:
4
Specific Gravity:
3.40
Crystal System:
Orthorhombic
Name:
Named for Richard JOHNson (1936-1998) and Frank WALKup (1943-1993), mineral preparators, National Museum of Natural History, Washington, D.C., USA.
Unique Identifiers
Mindat ID:
2108
Long-form identifier:
mindat:1:1:2108:7
GUID
(UUID V4):
(UUID V4):
fd35d3bc-d310-41f3-bfcb-d0b3018b6818
IMA Classification of Johnwalkite
Approved
IMA Formula:
K(Mn2+,Fe3+)2(Nb,Ta)O2(PO4)2 · 2(H2O,OH)
Approval year:
1985
First published:
1986
Classification of Johnwalkite
8.DJ.05
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
J : With large and medium-sized cations, (OH, etc.):RO4 = 1:1
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
J : With large and medium-sized cations, (OH, etc.):RO4 = 1:1
42.7.11.2
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
7 : (AB)2(XO4)Zq·xH2O
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
7 : (AB)2(XO4)Zq·xH2O
22.5.14
22 : Phosphates, Arsenates or Vanadates with other Anions
5 : Phosphates, arsenates or vanadates with chromate, molybdate, niobate or tantalate
22 : Phosphates, Arsenates or Vanadates with other Anions
5 : Phosphates, arsenates or vanadates with chromate, molybdate, niobate or tantalate
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference |
|---|---|---|
| Jwk | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Johnwalkite
Vitreous
Transparency:
Opaque
Colour:
Very dark reddish brown
Streak:
Medium greenish yellow
Hardness:
4 on Mohs scale
Tenacity:
Brittle
Cleavage:
Distinct/Good
Good on {001} and {100}; poor on {010}
Good on {001} and {100}; poor on {010}
Density:
3.40(3) g/cm3 (Measured) 3.44 g/cm3 (Calculated)
Optical Data of Johnwalkite
Type:
Biaxial (+)
RI values:
nα = 1.748(5) nβ = 1.763(5) nγ = 1.840(1)
2V:
Measured: 53° (2), Calculated: 50°
Max Birefringence:
δ = 0.092
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
and does not take into account mineral colouration.
Surface Relief:
High
Dispersion:
r > v strong
Optical Extinction:
X = c; Y = a; Z = b.
Pleochroism:
Strong
Comments:
X = blue-green; Y = yellow to pale brown; Z = brown.
Comments:
Absorption: X >> Z >> Y.
Chemistry of Johnwalkite
Mindat Formula:
K(Mn2+,Fe2+,Fe3+)2(Nb5+,Ta5+)(PO4)2O2 · 2(H2O,OH)
Crystallography of Johnwalkite
Crystal System:
Orthorhombic
Class (H-M):
mm2 - Pyramidal
Cell Parameters:
a = 7.516(4) Å, b = 10.023(8) Å, c = 6.502(4) Å
Ratio:
a:b:c = 0.75 : 1 : 0.649
Unit Cell V:
489.81 ų (Calculated from Unit Cell)
Z:
1
Comment:
Space Group: [Pb21m] (by analogy to olmsteadite).
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 6.01 Å | (100) |
| 3.005 Å | (80) |
| 3.054 Å | (70) |
| 2.862 Å | (70) |
| 6.51 Å | (40) |
| 2.563 Å | (40) |
| 7.54 Å | (30) |
Comments:
Champion Mine, South Dakota, USA. Data are from the type description.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 22 : Hydration and low-𝑇 subsurface aqueous alteration (see also #23) |
Type Occurrence of Johnwalkite
General Appearance of Type Material:
Prismatic, dark reddish-brown radially arranged crystals to 6 mm.
Place of Conservation of Type Material:
National Museum of Natural History, Washington, D.C., USA, 162676.
Geological Setting of Type Material:
Pegmatite.
Associated Minerals at Type Locality:
Reference:
Dunn, P. J.; Peacor, D. R.; Sturman, D. B.; Ramik, R. A.; Roberts, W. L.; Nelen, J. A. (1986): Johnwalkite, the manganese analog of olmsteadite, from South Dakota. Neues Jahrbuch für Mineralogie, Monatshefte 1986, 115-120.
Synonyms of Johnwalkite
Other Language Names for Johnwalkite
Related Minerals - Strunz-mindat Grouping
| 8.DJ.05 | Olmsteadite | KFe2+2(Nb5+,Ta5+)(PO4)2O2 · 2H2O |
| 8.DJ.10 | Gatumbaite | CaAl2(PO4)2(OH)2 · H2O |
| 8.DJ.15 | Camgasite | CaMg(AsO4)(OH) · 5H2O |
| 8.DJ.20 | Phosphofibrite | (H2O,K)3.5Fe8(PO4)6(OH)7 · 5H2O |
| 8.DJ.20 | Meurigite-K | KFe3+8(PO4)6(OH)7 · 6.5H2O |
| 8.DJ.20 | Meurigite-Na | NaFe3+8(PO4)6(OH)7 · 6.5H2O |
| 8.DJ.25 | Jungite | Ca2Zn4Fe3+8(PO4)9(OH)9 · 16H2O |
| 8.DJ.30 | Wycheproofite | NaAlZr(PO4)2(OH) · H2O |
| 8.DJ.35 | Ercitite | Na2Mn3+2(PO4)2(OH)2 · 4H2O |
| 8.DJ.40 | Mrázekite | Bi2Cu3(PO4)2O2(OH)2 · H2O |
| 8.DJ.45 | Attikaite | Ca3Cu2Al2(AsO4)4(OH)4 · 2H2O |
| 8.DJ.50 | Mengeite | Ba(Mg,Mn2+)Mn3+4(PO4)4(OH)4 · 4H2O |
Other Information
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Internet Links for Johnwalkite
mindat.org URL:
https://www.mindat.org/min-2108.html
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References for Johnwalkite
Reference List:
Localities for Johnwalkite
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
USA (TL) | |
| Dunn et al. (1986) +1 other reference |
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Champion Mine, Keystone, Keystone Mining District, Pennington County, South Dakota, USA