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Ahlfeldite
A valid IMA mineral species - grandfathered
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About Ahlfeldite
Friedrich Ahlfeld
Formula:
Ni(SeO3) · 2H2O
May contain minor Co.
Colour:
apple-green, brown, pink, yellowish
Lustre:
Vitreous
Hardness:
2 - 2½
Specific Gravity:
3.37
Crystal System:
Monoclinic
Name:
Named in honor of Friedrich Ahlfeld ( 6 October 1892, Marburg, German Empire - 9 January 1982, Cochabamba, Bolivia), German-Bolivian mining engineer and geologist, known as the "Father of Bolivian Geology." He built several important collections of Bolivian minerals.
Type Locality:
Isostructural with:
This page provides mineralogical data about Ahlfeldite.
Unique Identifiers
Mindat ID:
61
Long-form identifier:
mindat:1:1:61:7
IMA Classification of Ahlfeldite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
Ni2+Se4+O3·2H2O
Classification of Ahlfeldite
4.JH.10
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
J : Arsenites, antimonites, bismuthites, sulfites, selenites, tellurites; iodates
H : Selenites without additional anions, with H2O
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
J : Arsenites, antimonites, bismuthites, sulfites, selenites, tellurites; iodates
H : Selenites without additional anions, with H2O
Dana 7th ed.:
34.2.3.3
34.2.3.3
34 : SELENITES, TELLURITES AND SULFITES
2 : A(XO3)·xH2O
34 : SELENITES, TELLURITES AND SULFITES
2 : A(XO3)·xH2O
28.1.13
28 : Selenites, Selenates, Tellurites, and Tellurates
1 : Selenites
28 : Selenites, Selenates, Tellurites, and Tellurates
1 : Selenites
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 |
|---|---|---|
| Afe | 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 Ahlfeldite
Vitreous
Transparency:
Transparent
Colour:
Apple-green, brown, pink, yellowish
Comment:
Becomes more pink with increasing cobalt content.
Streak:
Pale green, white
Hardness:
2 - 2½ on Mohs scale
Tenacity:
Brittle
Cleavage:
Imperfect/Fair
Fair on {110}{103}
Fair on {110}{103}
Density:
3.37(2) g/cm3 (Measured) 3.51 g/cm3 (Calculated)
Optical Data of Ahlfeldite
Type:
Biaxial (-)
RI values:
nα = 1.709(1) nβ = 1.752(1) nγ = 1.787(2)
2V:
Measured: 85° , Calculated: 82°
Max. Birefringence:
δ = 0.078
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.
Dispersion:
r < v strong
Optical Extinction:
Y = b; Z ∧ c = –16°.
Pleochroism:
Visible
Comments:
X = pale green; Y = pale pink; Z = pink.
Chemistry of Ahlfeldite
Mindat Formula:
Ni(SeO3) · 2H2O
May contain minor Co.
May contain minor Co.
Element Weights:
Elements listed:
Common Impurities:
Co
Crystallography of Ahlfeldite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/c
Setting:
P21/n
Cell Parameters:
a = 7.53 Å, b = 8.76 Å, c = 6.43 Å
β = 99.08°
β = 99.08°
Ratio:
a:b:c = 0.86 : 1 : 0.734
Unit Cell V:
418.83 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Rare crystals to 1mm, crusts, spherical aggregates
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Show
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
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Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
Remove metal-metal sticks
Display Options
Black Background | White Background
Perspective On | Perspective Off
2D | Stereo | Red-Blue | Red-Cyan
Black Background | White Background
Perspective On | Perspective Off
2D | Stereo | Red-Blue | Red-Cyan
View
CIF File Best | x | y | z | a | b | c
CIF File Best | x | y | z | a | b | c
Rotation
Stop | Start
Stop | Start
Labels
Console Off | On | Grey | Yellow
Console Off | On | Grey | Yellow
Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0014382 | Ahlfeldite | Larranaga A, Mesa J L, Pizarro J L, Pena A, Chapman J P, Arriortua M I, Rojo T (2005) Thermal, spectroscopic and magnetic properties of the CoxNi1-x(SeO3)*2H2O (x = 0, 0.4, 1) phases crystal structure of Co0.4Ni0.6(SeO3)*2H2O Materials Research Bulletin 40 781-793 | 2005 | synthetic | 0 | 293 | |
| 0014846 | Ahlfeldite | Wildner M (1990) Crystal structure refinements of synthetic cobaltomenite (CoSeO3*2H2O) and ahlfeldite (NiSeO3*2H2O) Neues Jahrbuch fur Mineralogie, Monatshefte 1990 353-362 | 1990 | synthetic | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 5.69 Å | (100) |
| 3.426 Å | (80) |
| 2.992 Å | (75) |
| 2.190 Å | (75) |
| 3.772 Å | (60) |
| 2.719 Å | (60) |
| 2.354 Å | (50) |
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] |
Geological Setting:
Alteration product of nickel sulfides and selenides
Type Occurrence of Ahlfeldite
General Appearance of Type Material:
Rare crystals, to 1 mm; in crystalline crusts and spherical aggregates.
Place of Conservation of Type Material:
Natural History Museum, London
Geological Setting of Type Material:
alteration product of nickel-bearing selenides and sulfides.
Associated Minerals at Type Locality:
Other Language Names for Ahlfeldite
Dutch:Ahlfeldiet
French:Ahlfeldite
German:Ahlfeldit
Italian:Ahlfeldite
Japanese:アールフェルド石
Norwegian:Ahlfeldit
Russian:Альфильдит
Spanish:Ahlfeldita
Relationship of Ahlfeldite to other Species
Forms a series with:
Common Associates
Associations Based on Photo Data:
| 17 photos of Ahlfeldite associated with Chalcomenite | CuSeO3 · 2H2O |
| 8 photos of Ahlfeldite associated with Alfredopetrovite | Al2(Se4+O3)3 · 6H2O |
| 3 photos of Ahlfeldite associated with Felsőbányaite | Al4(SO4)(OH)10 · 4H2O |
| 2 photos of Ahlfeldite associated with Molybdomenite | PbSeO3 |
| 2 photos of Ahlfeldite associated with Goethite | Fe3+O(OH) |
| 2 photos of Ahlfeldite associated with Kruťaite | CuSe2 |
| 1 photo of Ahlfeldite associated with Penroseite | (Ni,Co,Cu)Se2 |
| 1 photo of Ahlfeldite associated with Anglesite | PbSO4 |
El Dragón mine, Porco Municipality, Antonio Quijarro Province, Potosí, Bolivia