Engelhauptite
A valid IMA mineral species
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About Engelhauptite
Formula:
KCu3(V2O7)(OH)2Cl
Colour:
Yellow-brown to brown, typically with an olive green hue
Lustre:
Vitreous
Specific Gravity:
3.86 (Calculated)
Crystal System:
Hexagonal
Name:
Named after the German amateur mineralogist and mineral collector Bernd Engelhaupt (born 1946), who found the mineral.
Structurally related to volborthite, and can be considered as its analogue resulting from the replacement of H2O molecules by the equal amounts of K+ and Cl− ions (Pekov et al 2015).
Unique Identifiers
Mindat ID:
43875
Long-form identifier:
mindat:1:1:43875:9
IMA Classification of Engelhauptite
Classification of Engelhauptite
8.FB.05
8 : PHOSPHATES, ARSENATES, VANADATES
F : Polyphosphates, Polyarsenates, [4]-Polyvanadates
B : Polyphosphates, etc., with OH only
8 : PHOSPHATES, ARSENATES, VANADATES
F : Polyphosphates, Polyarsenates, [4]-Polyvanadates
B : Polyphosphates, etc., with OH only
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 |
|---|---|---|
| Egh | 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 Engelhauptite
Vitreous
Transparency:
Transparent, Translucent
Colour:
Yellow-brown to brown, typically with an olive green hue
Streak:
Yellow
Hardness Data:
Could not be measured
Comment:
Could not be measured because of the very small size of individual grains and the porosity of the aggregates.
Tenacity:
Brittle
Cleavage:
None Observed
Fracture:
Irregular/Uneven
Density:
3.86 g/cm3 (Calculated)
Comment:
Could not be measured because of the very small size of individual grains and the porosity of the aggregates.
Optical Data of Engelhauptite
Type:
Uniaxial (+)
RI values:
nω = 1.978(4) nε = 2.021(4)
Max. Birefringence:
δ = 0.043
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 uniaxial interference figure - the conoscopic
(convergent-light, Bertrand-lens-in) view, for a grain cut with the optic axis
centred and vertical. The coloured rings are isochromatics, computed with the
same physics as the Michel-Lévy bar above; the dark cross is the isogyre.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
Chemistry of Engelhauptite
Mindat Formula:
KCu3(V2O7)(OH)2Cl
Element Weights:
Crystallography of Engelhauptite
Crystal System:
Hexagonal
Class (H-M):
6/mmm(6/m2/m2/m) - Dihexagonal Dipyramidal
Space Group:
P63/mmc
Setting:
P63/mmc
Cell Parameters:
a = 5.922(2) Å, c = 14.513(5) Å
Ratio:
a:c = 1 : 2.451
Unit Cell V:
440.78 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Spherulites (up to 0.2 mm in diameter) and bunches consisting of rough spindle-shaped crystals elongated parallel to [0001].
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 7.32 Å | (98) |
| 4.224 Å | (17) |
| 2.979 Å | (100) |
| 2.759 Å | (19) |
| 2.565 Å | (18) |
| 2.424 Å | (18) |
| 1.765 Å | (16) |
| 1.481 Å | (14) |
Comments:
From Type Description.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 47a : [Near-surface hydration of prior minerals] | |
| 47e : [Vanadates, chromates, manganates] |
Type Occurrence of Engelhauptite
General Appearance of Type Material:
Spherulites (up to 0.2 mm in diameter) and bunches consisting of rough spindle-shaped crystals. The crystals are up to 0.12 mm long and up to 0.04 mm thick.
Place of Conservation of Type Material:
Type material is deposited in the collections of the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, registration number 4309/1
Geological Setting of Type Material:
In cavities in nepheline basalts.
Associated Minerals at Type Locality:
Synonyms of Engelhauptite
Other Language Names for Engelhauptite
Dutch:Engelhauptiet
Common Associates
Associations Based on Photo Data:
| 2 photos of Engelhauptite associated with Volborthite | Cu3(V2O7)(OH)2 · 2H2O |
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) | 7.6203% | 2,362 | 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
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 Engelhauptite
mindat.org URL:
https://www.mindat.org/min-43875.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Engelhauptite
Reference List:
Williams, P. A., Hatert, F., Pasero, M., Mills, S. J. (2013) New minerals and nomenclature modifications approved in 2013. CNMNC Newsletter No 16. Mineralogical Magazine, 77 (6) 2695-2709 doi:10.1180/minmag.2013.077.6.01
Pekov, Igor V., Siidra, Oleg I., Chukanov, Nikita V., Yapaskurt, Vasiliy O., Britvin, Sergey N., Krivovichev, Sergey V., Schüller, Willi, Ternes, Bernd (2015) Engelhauptite, KCu3(V2O7)(OH)2Cl, a new mineral species from Eifel, Germany. Mineralogy and Petrology, 109 (6) 705-711 doi:10.1007/s00710-015-0400-8
Localities for Engelhauptite
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) | |
| Williams et al. (2013) +2 other references |
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Kahlenberg, Oberstadtfeld, Daun, Vulkaneifel, Rhineland-Palatinate, Germany