Akrochordite
A valid IMA mineral species - grandfathered
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About Akrochordite
Formula:
MnMn2Mn2(AsO4)2(OH)4(H2O)4
Simplified: (Mn2+)5(AsO4)2(OH)4 · 4H2O.
Type material contains some Mg replacing Mn.
Type material contains some Mg replacing Mn.
Colour:
Yellowish red-brown, pale to dark brown, pale pink,
Lustre:
Sub-Vitreous, Resinous, Dull
Hardness:
3½
Specific Gravity:
3.194 - 3.35
Crystal System:
Monoclinic
Member of:
Name:
Named by Gustav Flink in 1922 from Greek ακρόχορδον (akrochordon) = "a wart," in allusion to the appearance of its form of aggregation.
Isostructural with:
Unique Identifiers
Mindat ID:
72
Long-form identifier:
mindat:1:1:72:3
IMA Classification of Akrochordite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
Mn2+Mn2+2Mn2+2(As5+O4)2(OH)4(H2O)4
First published:
1922
Classification of Akrochordite
8.DD.10
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
D : With only medium-sized cations, (OH, etc.):RO4= 2:1
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
D : With only medium-sized cations, (OH, etc.):RO4= 2:1
42.4.1.1
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
4 : (AB)5(XO4)2Zq·xH2O
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
4 : (AB)5(XO4)2Zq·xH2O
20.8.11
20 : Arsenates (also arsenates with phosphate, but without other anions)
8 : Arsenates of Mn
20 : Arsenates (also arsenates with phosphate, but without other anions)
8 : Arsenates of Mn
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 |
|---|---|---|
| Akr | 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 Akrochordite
Sub-Vitreous, Resinous, Dull
Transparency:
Translucent
Colour:
Yellowish red-brown, pale to dark brown, pale pink,
Hardness:
3½ on Mohs scale
Tenacity:
Brittle
Cleavage:
Perfect
On {010} , perfect; a second, perpendicular to the first.
On {010} , perfect; a second, perpendicular to the first.
Density:
3.194 - 3.35 g/cm3 (Measured) 3.26 g/cm3 (Calculated)
Optical Data of Akrochordite
Type:
Biaxial (+)
RI values:
nα = 1.672 nβ = 1.676 nγ = 1.683
2V:
Measured: 45°
Birefringence:
0.011
Max. Birefringence:
δ = 0.011
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 relatively strong
Optical Extinction:
Y^c ~ 45°, X = b
Pleochroism:
Non-pleochroic
Chemistry of Akrochordite
Mindat Formula:
MnMn2Mn2(AsO4)2(OH)4(H2O)4
Simplified: (Mn2+)5(AsO4)2(OH)4 · 4H2O.
Type material contains some Mg replacing Mn.
Simplified: (Mn2+)5(AsO4)2(OH)4 · 4H2O.
Type material contains some Mg replacing Mn.
Element Weights:
Elements listed:
Crystallography of Akrochordite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/b
Setting:
P21/c
Cell Parameters:
a = 5.682 Å, b = 17.627 Å, c = 6.832 Å
β = 99.5°
β = 99.5°
Ratio:
a:b:c = 0.322 : 1 : 0.388
Unit Cell V:
674.89 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Crystals are prismatic to lathlike, elongated along [201], generally splayed or tapered, to 2 mm; may be in radial aggregates and subparallel sheaves. Typically as wartlike or spherical aggregates of minute crystals.
Crystal Structure
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Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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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) |
|---|---|---|---|---|---|---|---|
| 0001206 | Akrochordite | Moore P B, Sen Gupta P K, Schlemper E O (1989) Akrochordite, (Mn,Mg)5(OH)4(H2O)4(AsO4)2: A sheet structure with amphibole walls American Mineralogist 74 256-262 |  | 1989 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 8.79 Å | (80) |
| 5.31 Å | (35) |
| 4.40 Å | (100) |
| 3.62 Å | (40) |
| 3.112 Å | (35) |
| 3.062 Å | (35) |
| 2.750 Å | (50) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| High-? alteration and/or metamorphism | |
| 32 : Ba/Mn/Pb/Zn deposits, including metamorphic deposits |
Geological Setting:
in fractures in a metamorphosed zinc orebody (Sterling Hill, New Jersey, USA).
Type Occurrence of Akrochordite
General Appearance of Type Material:
Small, rounded wartlike aggregates
Place of Conservation of Type Material:
National Museum of Natural History, Washington, D.C., USA, 162614, R5396.
Chemical Analysis of Type Material:
| P2O5 | 0.42 % |
|---|---|
| As2O5 | 33.51 % |
| MnO | 38.98 % |
| Mn2O3 | 0.50 % |
| FeO | 0.46 % |
| MgO | 6.94 % |
| K2O | 0.55 % |
| Na2O | 1.18 % |
| CaO | 0.99 % |
| H2O | 16.78 % |
| Total: | 100.31 % |
Geological Setting of Type Material:
A rare mineral in hausmannite ore from a metamorphosed Fe–Mn orebody
Associated Minerals at Type Locality:
Synonyms of Akrochordite
Other Language Names for Akrochordite
Relationship of Akrochordite to other Species
Member of:
Other Members of Akrochordite Group:
| Guanacoite | MgCu2Mg2(AsO4)2(OH)4(H2O)4 | Mon. 2/m : P21/b |
| Vargite | MnCu2Mn2(AsO4)2(OH)4(H2O)4 | Mon. 2/m : P21/b |
Common Associates
Associations Based on Photo Data:
| 8 photos of Akrochordite associated with Eveite | Mn2+2(AsO4)(OH) |
| 4 photos of Akrochordite associated with Pyrochroite | Mn(OH)2 |
| 4 photos of Akrochordite associated with Sarkinite | Mn2+2(AsO4)(OH) |
| 4 photos of Akrochordite associated with Sussexite | Mn2+BO2(OH) |
| 4 photos of Akrochordite associated with Kraisslite | Zn3(Mn,Mg)25(Fe3+,Al)(As3+O3)2[(Si,As5+)O4]10(OH)16 |
| 4 photos of Akrochordite associated with Willemite | Zn2SiO4 |
| 3 photos of Akrochordite associated with Franklinite | Zn2+Fe3+2O4 |
| 2 photos of Akrochordite associated with Manganohörnesite | Mn2+3(AsO4)2 · 8H2O |
| 1 photo of Akrochordite associated with Hematolite | (Mn,Mg,Al,Fe3+)15(As5+O4)2(As3+O3)(OH)23 |
| 1 photo of Akrochordite associated with Långbanshyttanite | Pb2Mn2Mg(AsO4)2(OH)4 · 6H2O |
Related Minerals - Strunz-mindat Grouping
| 8.DD. | Penberthycroftite | [Al6(AsO4)3(OH)9(H2O)5] · 8H2O |
| 8.DD. | Bettertonite | [Al6(AsO4)3(OH)9(H2O)5] · 11H2O |
| 8.DD. | Vargite | MnCu2Mn2(AsO4)2(OH)4(H2O)4 |
| 8.DD. | Galeaclolusite | Al6(AsO4)3(OH)9(H2O)4 · 8H2O |
| 8.DD.05 | Luetheite | Cu2Al2(AsO4)2(OH)4 |
| 8.DD.05 | Chenevixite | Cu2Fe3+2(AsO4)2(OH)4 |
| 8.DD.10 | Guanacoite | MgCu2Mg2(AsO4)2(OH)4(H2O)4 |
| 8.DD.15 | 'UM1981-32-PO:FeH' | Fe2+Fe3+6(PO4)4-x[PO3(OH)]x(OH)8 · 4H2O |
| 8.DD.15 | Afmite | Al3(OH)4(H2O)3(PO4)(PO3OH) · H2O |
| 8.DD.15 | Aheylite | (Fe2+,Zn)Al6(PO4)4(OH)8 · 4H2O |
| 8.DD.15 | 'Coeruleolactite' | |
| 8.DD.15 | Faustite | ZnAl6(PO4)4(OH)8 · 4H2O |
| 8.DD.15 | Planerite | Al6(PO4)2(PO3OH)2(OH)8 · 4H2O |
| 8.DD.15 | Chalcosiderite | CuFe3+6(PO4)4(OH)8 · 4H2O |
| 8.DD.15 | Turquoise | CuAl6(PO4)4(OH)8 · 4H2O |
| 8.DD.20 | Eosphorite | Mn2+Al(PO4)(OH)2 · H2O |
| 8.DD.20 | Ernstite | (Mn2+,Fe3+)Al(PO4)(OH,O)2 · H2O |
| 8.DD.20 | Lefontite | Fe2Al2Be(PO4)2(OH)6 |
| 8.DD.20 | Childrenite | Fe2+Al(PO4)(OH)2 · H2O |
| 8.DD.25 | Kobokoboite | Al6(PO4)4(OH)6 · 11H2O |
| 8.DD.30 | Smamite | Ca2Sb(OH)4[H(AsO4)2] · 6H2O |
| 8.DD.35 | 'Gutsevichite' | Al3(PO4)2(OH)3 · 8H2O |
| 8.DD.40 | 'Laubmannite (of Moore)' | (Fe3+,Fe2+,M)8+x(OH,H2O)9(H2O)2(PO4)5, M = Fe3+, Cu2+ or other metal cation, x ~ 0.1. |
Fluorescence of Akrochordite
Not fluorescent
Other Information
Notes:
Readily soluble in dilute H2SO4, yielding a purple (lilac) solution.
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 Akrochordite
mindat.org URL:
https://www.mindat.org/min-72.html
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References for Akrochordite
Reference List:
Flink, Gustav (1922) Akrochordit, ett nytt mineral från Långbans grnvor. Geologiska Föreningen i Stockholm Förhandlingar, 44 (6) 773-776 doi:10.1080/11035892209444535
Localities for Akrochordite
Showing 5 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 | |
| Haack et al. (1987) |
Sweden (TL) | |
| Palache et al. (1951) +2 other references |
| Flink (1922) | |
| Langhof (2003) |
USA | |
| Dunn (1981) +1 other reference |
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Moss mine, Nordmark Odal Field, Filipstad, Värmland County, Sweden