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About RokühniteHide

FeCl2 · 2H2O
Colourless (transmitted light), light green
Specific Gravity:
Crystal System:
Named after Robert Kühn (1911–2000), German mineralogist, and professor at Kaliforschungs-Institut der Kali und Salz AG, Hannover, Germany.
The hydrated counterpart of lawrencite. Other approved ferrous-iron-bearing chlorides include droninoite and hibbingite. Compare the hydrated ferric-iron chloride minerals: 'hydromolysite', 'Unnamed (Fe Chloride Hydrate I)', and 'Unnamed (Fe Chloride Hydrate II)'.

Crystal structure (synthetic material) details/elements:
- polymeric chains of iron and chlorine ions, near‐square planar configuration
- 2 iron ions share single Cl ion
- water groups fill the remaining octahedral positions about the iron ion
- hydrogen bonds involving water groups link adjacent chains, in direction || c.

Classification of RokühniteHide

First Published:

B : Simple halides, with H2O
B : M:X = 1:2

2 : AX2

8 : Halides - Fluorides, Chlorides, Bromides and Iodides; also Fluoborates and Fluosilicates
11 : Halides of Fe and Ni

Physical Properties of RokühniteHide

Colourless (transmitted light), light green
brown when oxidized
not determined
Very Good
{100}; also good on {010}
2.35 g/cm3 (Measured)    2.35 g/cm3 (Calculated)

Optical Data of RokühniteHide

Biaxial (+)
RI values:
nα = 1.605 nβ = 1.633 nγ = 1.702
Measured: 64° , Calculated: 68°
Max Birefringence:
δ = 0.097
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
strong (r ≤ v)

Chemical Properties of RokühniteHide

FeCl2 · 2H2O
Common Impurities:

Crystallography of RokühniteHide

Crystal System:
Cell Parameters:
a = 7.396(1) Å, b = 8.458(2) Å, c = 3.638(1) Å
β = 97.68(2)°
a:b:c = 0.874 : 1 : 0.43
Unit Cell V:
225.54 ų (Calculated from Unit Cell)
contact, on {201}
C2/m, C2 or Cm

X-Ray Powder DiffractionHide

Powder Diffraction Data:
5.536 Å(100)
2.762 Å(74)
4.228 Å(62)
2.415 Å(55)
2.892 Å(54)
2.744 Å(30)
2.096 Å(30)

Type Occurrence of RokühniteHide

General Appearance of Type Material:
rare thin plates, commonly comprising fibers, with dominating {110} form and a number of other forms present, up to 300 µm
Geological Setting of Type Material:
secondary, in fissures within earlier K-rich salt beds
Associated Minerals at Type Locality:
von Hodenberg, R., von Struensee, G. (1980) Rokühnite, FeCl2•2H2O, a new mineral. Neues Jahrb. Mineral. Monatsh.: 125-130.

Synonyms of RokühniteHide

Other Language Names for RokühniteHide


Common AssociatesHide

Associated Minerals Based on Photo Data:
4 photos of Rokühnite associated with CarnalliteKMgCl3 · 6H2O

Related Minerals - Nickel-Strunz GroupingHide

3.BB.05EriochalciteCuCl2 · 2H2OOrth. mmm (2/m 2/m 2/m)
3.BB.15BischofiteMgCl2 · 6H2OMon. 2/m : B2/m
3.BB.20NickelbischofiteNiCl2 · 6H2OMon.
3.BB.25SinjariteCaCl2 · 2H2OTet.
3.BB.30AntarcticiteCaCl2 · 6H2OTrig. 3 2 : P3 2 1
3.BB.35TachyhydriteCaMg2Cl6 · 12H2OTrig.

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

8.11.2HydromolysiteFeCl3 · 6H2O
8.11.5ErythrosideriteK2[Fe3+Cl5(H2O)]Orth. mmm (2/m 2/m 2/m) : Pnma
8.11.6RinneiteK3Na[FeCl6]Trig. 3m (3 2/m) : R3c
8.11.7Kremersite(NH4,K)2[Fe3+Cl5(H2O)]Orth. mmm (2/m 2/m 2/m)
8.11.8IowaiteMg6Fe3+2(OH)16Cl2 · 4H2OTrig. 3m (3 2/m) : R3m
8.11.9NickelbischofiteNiCl2 · 6H2OMon.
8.11.10Lawrencite(Fe2+,Ni)Cl2Trig. 3m (3 2/m) : R3m

Other InformationHide

water-soluble; topotactical hydration and rapid oxidation in air
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for RokühniteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Morosin, B., Graeber, E.J. (1965) Crystal Structures of Manganese(II) and Iron(II) Chloride Dihydrate. J. Chem. Phys.: 42: 898.
von Hodenberg, R., von Struensee, G. (1980) Rokühnite, FeCl2•2H2O, a new mineral. Neues Jahrb. Mineral. Monatsh.: 125-130.
American Mineralogist (1981): 66: 219.
Anthony, J.W., Bideaux, R.A., Bladh, K.W. and Nichols, M.C., Eds. Handbook of Mineralogy, Mineralogical Society of America, Chantilly, VA 20151-1110, USA. (2016).

Internet Links for RokühniteHide

Localities for RokühniteHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for 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). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (eg from pseudomorphs.)

All localities listed without proper references should be considered as questionable.
Czech Republic
  • Moravian-Silesian Region
    • Karviná District
      • Orlová
Matýsek D., Jirásek J., Osovský M., Skupien P.. Minerals formed by the weathering of sulfides in mines of the Czech part of the Upper Silesian Basin. Mineralogical Magazine, 2014, 78, 5, 1265-1286.
  • Lower Saxony
    • Hildesheim
      • Diekholzen Potash works
Andreas Gerstenberg collection
      • Giesen
Aufschluss 1987(4), 114
Aufschluss 87/4
  • Silesian Voivodeship
    • Wodzisław Co.
      • Radlin
Łukasz Kruszewski (2012) Unique chloride assemblage of exhalative origin from burning coal-mining dump in Radlin (Rybnik Coal Area, S Poland). Mineralogical Society of Poland Special Papers 40
  • Zhytomyr Oblast
Lyckberg, P., Chornousenko, V. & Wilson, W. E. (2009): Volodarsk-Volynski, Zhitomir Oblast, Ukraine. Mineralogical Record, 40, 473-506.
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