Metakahlerite

Fe2+(UO2)2(AsO4)2 · 8H2O
IMA status
  • Approved
  • Grandfathered
IMA symbol
Mkah
Discovered
1958
Also known as
  • Metakahleriet

Where it forms, where it's found

Type locality
Sophia Mine
  1. Böckelsbach valley
  2. Wittichen
  3. Schenkenzell
  4. Rottweil
  5. Freiburg Region
  6. Baden-Württemberg
  7. Germany

48.3333°, 8.3333°

18recorded occurrences
Source · OpenStreetMap

Radioactivity

Physical

Hardness
123456789102 – 3/ 10 MOHS
  1. 1Talc
  2. 2Gypsum
  3. 3Calcite
  4. 4Fluorite
  5. 5Apatite
  6. 6Orthoclase
  7. 7Quartz
  8. 8Topaz
  9. 9Corundum
  10. 10Diamond
Colour
sulphur yellow
Streak
pale yellow
Cleavage
Perfect

Optical

Optical type
Uniaxial (-)
Refractive index
1.608 – 1.642
Surface relief
Moderate
Principal indices
nω 1.642 · nε 1.608
Michel-Lévy diagramhighlighted lineδ = 0.0340
Attainable Michel-Lévy rangeΔ ∈ [0, t·δmax]340 nm1st order
Δ = 0Δmax
Thin-section mosaic70 grains · random 3D orientations
PPLpleochroism per grain
XPLindependent extinctions · rotate the stage
Interference simulatorsingle grain · PPL ↔ XPL
PPLpleochroism only · colour blends on rotation
XPLinterference colour · extinct every 90°
Retardation340 nm
Order1st order
XPL colour

Crystallography

Crystal system
Triclinic
Space group
#2
Cell parameters
a = 7.2072 Å · b = 9.8242 Å · c = 13.2708 Å
Cell angles
α = 75.37 ° · β = 84.024 ° · γ = 81.839 °
Ratio a:b:c
1 : 1.363 : 1.841
Crystal structure

Chemical composition

Constituent elements
Mass composition breakdown
ElementAtoms At. mass g/mol Mass g/molMass share
92UUraniumUranium2238.029476.058
46.77%
8OOxygenOxygen2015.999319.980
31.44%
33AsArsenicArsenic274.922149.844
14.72%
26FeIronIron155.84555.845
5.49%
1HHydrogenHydrogen161.00816.128
1.58%
Total1017.855100.00%

Mass share = atoms × atomic mass ÷ molar mass × 100

From IMA formula

Synonyms

  • Metakahleriet

In other languages

German
Metakahlerit
Italian
Metakahlerite

Classification

Strunz
10th ed.

8.EB.10

  • 8Phosphates, Arsenates, VanadatesClass
  • 8.EUranyl phosphates and arsenatesDivision
  • 8.EBUO2:RO4 = 1:1Group
  • 8.EB.10MetakahleriteSpecies
Dana
8th ed.

40.2a.15.02

  • 40Hydrated Normal Phosphates, Arsenates and VanadatesClass
  • 40.2aAB2(XO4)2·xH2O, containing (UO2)2+Type
  • 40.2a.15— unnamed intermediate level —Group
  • 40.2a.15.02MetakahleriteSpecies
CIM

20.7.18

  • 20Arsenates (also arsenates with phosphate, but without other anions)Class
  • 20.7Arsenates of UGroup
  • 20.7.18MetakahleriteSpecies

Group, growth & confusion

Literature, links & citation

Citations
  1. 1958Walenta, Kurt (1958) Die sekundären Uranmineralien des Schwarzwaldes. Jahreshefte des geologischen Landesamtes in Baden-Württemberg: 3: 17-51.
  2. 1960Fleischer, M. F. (1960) New Mineral Names; New data; Redefinition of mineral. American Mineralogist, 45 (1-2). 252-258
  3. 1964Walenta, Kurt, Walenta, Kurt (1964) Beiträge zur Kenntnis seltener Arsenatmineralien unter besonderer Berücksichtigung von Vorkommen des Schwarzwaldes. 1. Folge. [Rare arsenate minerals with special consideration of occurrences in the Black Forest. Part I]. Tschermaks Mineralogische und Petrographische Mitteilungen, 9 (1). 111-174 doi:10.1007/bf01127780DOI: 10.1007/bf01127780
  4. 1986Vochten, R., De Grave, E., Pelsmaekers, J. (1986) Synthesis, crystallographic and spectroscopic data, solubility, and electrokinetic properties of metakahlerite and its Mn analogue. American Mineralogist, 71 (7-8) 1037-1044
  5. 2004Locock, A. J., Burns, P. C., Flynn, T. M. (2004) Divalent transition metals and magnesium in structures that contain the autunite-type sheet. The Canadian Mineralogist, 42 (6) 1699-1718 doi:10.2113/gscanmin.42.6.1699 DOI: 10.2113/gscanmin.42.6.1699
Cite this entry
@misc{mineral2026,
  author    = {Mineral Index editorial board},
  title     = {Metakahlerite — Mineral Index},
  year      = {2026},
  url       = {https://mineralindex.org/minerals/metakahlerite-2676},
  note      = {Accessed 2026-05-11}
}