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Akrochordite

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Långban, Filipstad, Värmland, Sweden
© Knut Eldjarn

Discuss Akrochordite



Formula:
(Mn
2+
 
,Mg)
 
5
(AsO
 
4
)
 
2
(OH)
 
4
 · 4H
 
2
O
System:MonoclinicColour:Yellowish red-brown, ...
Hardness:3½
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:Guanacoite


A rare (Mn,Mg)-arsenate isotypic with Guanacoite.

Classification of Akrochordite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:7/D.16-30
Nickel-Strunz 10th (pending) edition ID: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
Dana 8th edition ID:42.4.1.1

42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
4 : (AB)5(XO4)2Zq·xH2O
Hey's CIM Ref.:20.8.11

20 : Arsenates (also arsenates with phosphate, but without other anions)
8 : Arsenates of Mn
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Type Occurrence of Akrochordite

Type Locality:Långban, Filipstad, Värmland, Sweden
Place of Conservation of Type Material:National Museum of Natural History, Washington, D.C., USA, 162614, R5396.
Year of Discovery:1922
Geological Setting of type material:A rare mineral in hausmannite ore from a metamorphosed Fe–Mn orebody
Associated Minerals at type locality:
PyrochroiteHausmanniteEveiteBrandtiteBaryte

Occurrences of Akrochordite

Geological Setting:in fractures in a metamorphosed zinc orebody (Sterling Hill, New Jersey, USA).

Physical Properties of Akrochordite

Lustre:Sub-Vitreous, Resinous, Dull
Diaphaneity (Transparency):Translucent
Colour:Yellowish red-brown, pale to dark brown, pale pink,
Hardness (Mohs):3½
Tenacity:Brittle
Cleavage:Perfect
On {010} , perfect; a second, perpendicular to the first.
Density (measured):3.194 - 3.35 g/cm3
Density (calculated):3.26 g/cm3

Crystallography of Akrochordite

Crystal System:Monoclinic
Class (H-M):2/m - Prismatic
Space Group:P21/b {P1 1 21/b} {P21/c} {P1 21/c 1} {P21/a}
Space Group Setting:P21/c
Cell Parameters:a = 5.682Å, b = 17.627Å, c = 6.832Å
β = 99.5°
Ratio:a:b:c = 0.322 : 1 : 0.388
Unit Cell Volume: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.
X-Ray Powder Diffraction:
d-spacingIntensity
8.79 (80)
5.31 (35)
4.40 (100)
3.62 (40)
3.112 (35)
3.062 (35)
2.750 (50)

Optical Data of Akrochordite

Type:Biaxial (+)
RI values: nα = 1.672 nβ = 1.676 nγ = 1.683
2V:Measured: 45°
Birefringence:0.011
Maximum Birefringence:δ = 0.011

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:High
Dispersion:r < v relatively strong
Optical Extinction:Y^c ~ 45°, X = b
Pleochroism:Non-pleochroic

Chemical Properties of Akrochordite

Formula:
(Mn
2+
 
,Mg)
 
5
(AsO
 
4
)
 
2
(OH)
 
4
 · 4H
 
2
O
Essential elements:As, H, Mn, O
All elements listed in formula:As, H, Mg, Mn, O

Relationship of Akrochordite to other Species

Common Associates:
SarkiniteChlorophoeniciteChlorophoenicite
Related Minerals - Nickel-Strunz Grouping):

- +
8.DD.05Chenevixite
Cu
 
2
Fe
3+
2
(AsO
 
4
)
 
2
(OH)
 
4
8.DD.05Luetheite
Cu
 
2
Al
 
2
(AsO
 
4
)
 
2
(OH)
 
4
8.DD.10Guanacoite
Cu
 
2
Mg
 
3
(AsO
 
4
)
 
2
(OH)
 
4
 · 4H
 
2
O
8.DD.15Aheylite
(Fe
2+
 
,Zn)Al
 
6
(PO
 
4
)
 
4
(OH)
 
8
 · 4H
 
2
O
8.DD.15Chalcosiderite
Cu(Fe
3+
 
,Al)
 
6
(PO
 
4
)
 
4
(OH)
 
8
 · 4H
 
2
O
8.DD.15Faustite
(Zn,Cu)Al
 
6
(PO
 
4
)
 
4
(OH)
 
8
 · 4H
 
2
O
8.DD.15Planerite
Al
 
6
(PO
 
4
)
 
2
(HPO
 
4
)
 
2
(OH)
 
8
 · 4 H
 
2
O
8.DD.15Turquoise
Cu(Al,Fe
3+
 
)
 
6
(PO
 
4
)
 
4
(OH)
 
8
 · 4H
 
2
O
8.DD.15Afmite
Al
 
3
(OH)
 
4
(H2O)
 
3
(PO
 
4
)(PO
 
3
OH) · H2O
8.DD.20Childrenite
(Fe
2+
 
,Mn
2+
 
)Al(PO
 
4
)(OH)
 
2
 · H
 
2
O
8.DD.20Eosphorite
(Mn
2+
 
,Fe
2+
 
)Al(PO
 
4
)(OH)
 
2
 · H
 
2
O
8.DD.20Ernstite
(Mn
2+
 
,Fe
3+
 
)Al(PO
 
4
)(OH,O)
 
2
 · H
 
2
O
Related Minerals - Hey's Index Grouping:

- +
20.8.1Sarkinite
Mn
2+
2
(AsO
 
4
)(OH)
20.8.2Eveite
Mn
2+
2
(AsO
 
4
)(OH)
20.8.3Arsenoclasite
Mn
2+
5
(AsO
 
4
)
 
2
(OH)
 
4
20.8.4Flinkite
Mn
2+
2
Mn
3+
 
(AsO
 
4
)(OH)
 
4
20.8.5Jarosewichite
Mn
2+
3
Mn
3+
 
(AsO
 
4
)(OH)
 
6
20.8.6Allactite
Mn
2+
7
(AsO
 
4
)
 
2
(OH)
 
8
20.8.7Krautite
Mn(HAsO
 
4
) · H
 
2
O
20.8.8Synadelphite
Mn
2+
9
(As
5+
 
O
 
4
)
 
2
(As
3+
 
O
 
3
)(OH)
 
9
 · 2H
 
2
O
20.8.9Sterlinghillite
Mn
 
3
(AsO
 
4
)
 
2
 · 4H
 
2
O
20.8.10Geigerite
Mn
2+
5
(AsO
 
4
)
 
2
(HAsO
 
4
)
 
2
 · 10H
 
2
O
20.8.12Manganohörnesite
(Mn,Mg)
 
3
(AsO
 
4
)
 
2
 · 8H
 
2
O
20.8.13Fluckite
CaMn
2+
 
(HAsO
 
4
)
 
2
 · 2H
 
2
O
20.8.14Brandtite
Ca
 
2
(Mn
2+
 
,Mg)(AsO
 
4
)
 
2
 · 2H
 
2
O
20.8.15Parabrandtite
Ca
 
2
Mn
2+
 
(AsO
 
4
)
 
2
 · 2H
 
2
O
20.8.16Wallkilldellite-(Mn)
Ca
 
2
Mn
2+
3
(AsO
 
4
)
 
2
(OH)
 
4
 · 9H
 
2
O
20.8.17Berzeliite
NaCa
 
2
(Mg,Mn
2+
 
)
 
2
(AsO
 
4
)
 
3
20.8.18Manganberzeliite
(Ca,Na)
 
3
(Mn
2+
 
,Mg)
 
2
(AsO
 
4
)
 
3
20.8.19Magnesiochlorophoenicite
(Mg,Mn)
 
3
Zn
 
2
(AsO
 
4
)(OH,O)
 
6
20.8.20Villyaellenite
MnMn
 
2
Ca
 
2
(AsO
 
4
)
 
2
(HAsO
 
4
)
 
2
 · 4H
 
2
O
20.8.21Hematolite
(Mn,Mg,Al)
 
15
(As
5+
 
O
 
4
)
 
2
(As
3+
 
O
 
3
)(OH)
 
23
20.8.22Grischunite
NaCa
 
2
Mn
2+
5
Fe
3+
 
(AsO
 
4
)
 
6
 · 2H
 
2
O

Other Names for Akrochordite

Synonyms:
AchrochorditeAcrochordite
Other Languages:
German:Achrochordit
Acrochordit
Akrochordit
Russian:Акрохордит
Spanish:Achrochordita
Acrochordita
Akrochordita

Other Information

Fluorescence in UV light:Not fluorescent
Other Information:Readily soluble in dilute H2SO4, yielding a purple (lilac) solution.
Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Akrochordite

Reference List:

- +
Flink (1922) Geologiska Föeningens I Stockholm. Förhandlinger, Stockholm: 44: 773 (as Acrochordite).

Almström (1923) Geologiska Föeningens I Stockholm. Förhandlinger, Stockholm: 45: 117.

American Mineralogist (1923): 8: 167.

Barth and Berman (1930) Chemie der Erde, Jena: 5: 41.

Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124 pp.: 927.

Moore, P.B. (1968) Contributions to Swedish mineralogy. I. Studies on the basic arsenates of manganese: retzian, hemafibrite, synadelphite, arsenoclasite, arseniopleite, and akrochordite. Arkiv. Mineral. Geol., 4(5), 425–444.

American Mineralogist (1968): 53: 1779.

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.

Internet Links for Akrochordite

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    • Localities for Akrochordite

    The 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.
    Hide Locality List
    (TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
    Germany
     
    • Lower Saxony
      • Harz
        • Clausthal-Zellerfeld
          • Bad Grund
            • Wiemannsbucht
    		Haack, U., Schnorrer-Koehler, G. & Lueders, V. (1987): Seltenerd-Minerale aus hydrothermalen Gängen des Harzes. Chemie der Erde 47, 41-45 (in German).
    Sweden
     
    • Värmland
      • Filipstad
    		Geologiska Föeningens I Stockholm. Förhandlinger, Stockholm (1922) 44, 773; Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: 927; Nysten, P., Holtstam, D. and Jonsson, E. (1999) The Långban minerals. In Långban - The mines,their minerals, geology and explorers (D. Holtstam and J. Langhof, eds.), Swedish Museum of Natural History and Raster Förlag, Stockholm & Chr. Weise Verlag, Munich, pp. 89-183.
        • Nordmark (Nordmarksberg)
    		No reference listed
    USA
     
    • New Jersey
      • Sussex Co.
        • Franklin Mining District
          • Ogdensburg
            • Sterling Hill
    		Dunn, P.J. (1981) Mineralogical Magazine: 44: 235-236; Dunn, Pete J. (1995): Franklin and Sterling Hill New Jersey: the world’s most magnificent mineral deposits, part : 5: 655-656.
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