Rotherkopfite
A valid IMA mineral species
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About Rotherkopfite
Formula:
KNa2Fe2+(Fe2+)2(Ti1.5Fe2+0.5)[Si4O12]2
Rotherkopfite is a Li-free member of the neptunite group.
Colour:
dark brownish red
Lustre:
Vitreous
Hardness:
4½
Specific Gravity:
3.20
Crystal System:
Monoclinic
Member of:
Name:
Named for the type locality
Structure determined
Until now, the M3 site has been dominated by Li+; rotherkopfite is the first mineral with the neptunite structure in which the M3 site is dominated by Fe2+ rather than Li+.
Until now, the M3 site has been dominated by Li+; rotherkopfite is the first mineral with the neptunite structure in which the M3 site is dominated by Fe2+ rather than Li+.
Unique Identifiers
Mindat ID:
471009
Long-form identifier:
mindat:1:1:471009:3
IMA Classification of Rotherkopfite
Approved
IMA Formula:
KNa2(Fe2+2.5Ti4+1.5)Fe2+(Si4O12)2
Approval year:
2023
Type description reference:
Kampf, A. R., Möhn, G., Ma, C., Rossman, G. R., Désor, J., Guan, Y. (2024) Rotherkopfite, KNa₂(Fe²⁺2.5Ti⁴⁺1.5)Fe²⁺(Si₄O₁₂)₂, a new neptunite-group mineral without essential lithium, from Rother Kopf, Eifel volcanic fields, Germany. European Journal of Mineralogy, 36 (4). 605-614 doi:10.5194/ejm-36-605-2024
Classification of Rotherkopfite
9.EH.05
9 : SILICATES (Germanates)
E : Phyllosilicates
H : Transitional structures between phyllosilicate and other silicate units
9 : SILICATES (Germanates)
E : Phyllosilicates
H : Transitional structures between phyllosilicate and other silicate units
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 for Standard |
|---|---|---|
| Rkp | 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 Rotherkopfite
Vitreous
Transparency:
Transparent
Colour:
Dark brownish red
Streak:
Light orange
Hardness:
4½ on Mohs scale
Tenacity:
Brittle
Cleavage:
None Observed
Fracture:
Conchoidal
Comment:
fracture curved
Density:
3.20(2) g/cm3 (Measured) 3.271 g/cm3 (Calculated)
Optical Data of Rotherkopfite
Type:
Biaxial (+)
RI values:
nα = 1.668(5) nβ = 1.678(5) nγ = 1.720(5)
2V:
Measured: 53.2° (6), Calculated: 53.1°
Max. Birefringence:
δ = 0.052
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
Very High (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Pleochroism:
Non-pleochroic
Chemistry of Rotherkopfite
Mindat Formula:
KNa2Fe2+(Fe2+)2(Ti1.5Fe2+0.5)[Si4O12]2
Rotherkopfite is a Li-free member of the neptunite group.
Rotherkopfite is a Li-free member of the neptunite group.
Element Weights:
Crystallography of Rotherkopfite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/b
Setting:
C2/c
Cell Parameters:
a = 16.460(2) Å, b = 12.5457(6) Å, c = 10.0487(7) Å
β = 115.669(7)°
β = 115.669(7)°
Ratio:
a:b:c = 1.312 : 1 : 0.801
Unit Cell V:
1,870.29 ų (Calculated from Unit Cell)
Z:
4
Twinning:
none observed
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 9.63 Å | (100) |
| 7.76 Å | (33) |
| 3.339 Å | (38) |
| 3.198 Å | (48) |
| 2.952 Å | (67) |
| 2.867 Å | (37) |
| 2.179 Å | (35) |
| 1.511 Å | (34) |
Reference:
Kampf, A. R., Möhn, G., Ma, C., Rossman, G. R., Désor, J., Guan, Y. (2024) Rotherkopfite, KNa₂(Fe²⁺2.5Ti⁴⁺1.5)Fe²⁺(Si₄O₁₂)₂, a new neptunite-group mineral without essential lithium, from Rother Kopf, Eifel volcanic fields, Germany. European Journal of Mineralogy, 36 (4). 605-614 doi:10.5194/ejm-36-605-2024
Type Occurrence of Rotherkopfite
General Appearance of Type Material:
equant to tabular crystals up to about 0.2 mm
Place of Conservation of Type Material:
In the collections of the Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA, catalogue number 76283
Geological Setting of Type Material:
cavities in a xenolith embedded in a vesicular alkaline basalt. presumed to have formed as the result of contact metasomatism of the xenolith by the alkaline basalt melt.
Associated Minerals at Type Locality:
Reference:
Kampf, A. R., Möhn, G., Ma, C., Rossman, G. R., Désor, J., Guan, Y. (2024) Rotherkopfite, KNa₂(Fe²⁺2.5Ti⁴⁺1.5)Fe²⁺(Si₄O₁₂)₂, a new neptunite-group mineral without essential lithium, from Rother Kopf, Eifel volcanic fields, Germany. European Journal of Mineralogy, 36 (4). 605-614 doi:10.5194/ejm-36-605-2024
Synonyms of Rotherkopfite
Other Language Names for Rotherkopfite
Dutch:Rotherkopfiet
German:Rotherkopfit
Relationship of Rotherkopfite to other Species
Member of:
Other Members of Neptunite Group:
| Magnesioneptunite | KNa2Li(Mg)2Ti2[Si4O12]2 | Mon. 2/m : B2/b |
| Manganoneptunite | KNa2Li(Mn2+)2Ti2[Si4O12]2 | Mon. m : Bb |
| Neptunite | KNa2Li(Fe2+)2Ti2[Si4O12]2 | Mon. m : Bb |
| Watatsumiite | KNa2Li(Mn2+)2V4+2[Si4O12]2 | Mon. m : Bb |
Related Minerals - Strunz-mindat Grouping
| 9.EH.05 | Manganoneptunite | KNa2Li(Mn2+)2Ti2[Si4O12]2 |
| 9.EH.05 | Magnesioneptunite | KNa2Li(Mg)2Ti2[Si4O12]2 |
| 9.EH.05 | Neptunite | KNa2Li(Fe2+)2Ti2[Si4O12]2 |
| 9.EH.05 | Watatsumiite | KNa2Li(Mn2+)2V4+2[Si4O12]2 |
| 9.EH.10 | Grumantite | Na(HSi2O5) · H2O |
| 9.EH.15 | Sarcolite | Na4Ca12Al8Si12O46(SiO4,PO4)(OH,H2O)4(CO3,Cl) |
| 9.EH.20 | Ussingite | Na2AlSi3O8OH |
| 9.EH.25 | Telyushenkoite | (Cs,Na,K)Na6[Be2Al3Si15O39]F2 |
| 9.EH.25 | Leifite | (Na,H2O)Na6[Be2Al2(Al,Si)Si15O39]F2 |
| 9.EH.25 | Eirikite | KNa6Be2(Si15Al3)O39F2 |
| 9.EH.30 | Nafertisite | Na3Fe2+10Ti2(Si6O17)2O2(OH)6F(H2O)2 |
| 9.EH.35 | Veblenite | KNa(Fe2+5Fe3+4Mn7)Nb4(Si2O7)2(Si8O22)2O6(OH)10(H2O)3 |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 0.0000% | 0 | α, β, γ |
| Thorium (Th) | 0.0000% | 0 | α, β, γ |
| Potassium (K) | 4.0685% | 1,261 | β, γ |
For comparison:
- Banana: ~15 Bq per fruit
- Granite: 1,000–3,000 Bq/kg
- EU exemption limit: 10,000 Bq/kg
Note: Risk is shown relative to daily recommended maximum exposure to non-background radiation of 1000 µSv/year. Note that natural background radiation averages around 2400 µSv/year so in reality these risks are probably extremely overstated! With infrequent handling and safe storage natural radioactive minerals do not usually pose much risk.
Interactive Simulator:
Note: The mass selector refers to the mass of radioactive mineral present, not the full specimen, also be aware that the matrix may also be radioactive, possibly more radioactive than this mineral!
Activity: –
| Distance | Dose rate | Risk |
|---|---|---|
| 1 cm | ||
| 10 cm | ||
| 1 m |
The external dose rate (D) from a radioactive mineral is estimated by summing the gamma radiation contributions from its Uranium, Thorium, and Potassium content, disregarding daughter-product which may have a significant effect in some cases (eg 'pitchblende'). This involves multiplying the activity (A, in Bq) of each element by its specific gamma ray constant (Γ), which accounts for its unique gamma emissions. The total unshielded dose at 1 cm is then scaled by the square of the distance (r, in cm) and multiplied by a shielding factor (μshield). This calculation provides a 'worst-case' or 'maximum risk' estimate because it assumes the sample is a point source and entirely neglects any self-shielding where radiation is absorbed within the mineral itself, meaning actual doses will typically be lower. The resulting dose rate (D) is expressed in microsieverts per hour (μSv/h).
D = ((AU × ΓU) + (ATh × ΓTh) + (AK × ΓK)) / r2 × μshield
Fluorescence of Rotherkopfite
No fluorescence was observed in either long- or short-wave ultraviolet illumination
Other Information
Notes:
At room temperature, rotherkopfite is insoluble in concentrated HCl.
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 Rotherkopfite
mindat.org URL:
https://www.mindat.org/min-471009.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Rotherkopfite
Reference List:
Bosi, Ferdinando, Hatert, Frédéric, Pasero, Marco, Mills, Stuart J. (2024) IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) – Newsletter 77. European Journal of Mineralogy, 36 (1). 165-172 doi:10.5194/ejm-36-165-2024
Kampf, A. R., Möhn, G., Ma, C., Rossman, G. R., Désor, J., Guan, Y. (2024) Rotherkopfite, KNa₂(Fe²⁺2.5Ti⁴⁺1.5)Fe²⁺(Si₄O₁₂)₂, a new neptunite-group mineral without essential lithium, from Rother Kopf, Eifel volcanic fields, Germany. European Journal of Mineralogy, 36 (4). 605-614 doi:10.5194/ejm-36-605-2024
Localities for Rotherkopfite
Showing 1 localities.
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.
Germany (TL) | |
| Bosi et al. (2024) +1 other reference |
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Rother Kopf, Roth, Gerolstein, Gerolstein, Vulkaneifel, Rhineland-Palatinate, Germany