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Gengenbachite

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Formula:
KFe
3+
3
(HPO
 
4
)
 
4
(H
 
2
PO
 
4
)
 
2
 · 6H
 
2
O
System:TrigonalColour:Pale brown
Hardness:2
Name:For the town of Gengenbach, adjacent to the type locality.
This page provides mineralogical data about Gengenbachite.

Classification of Gengenbachite

IMA status:Approved 2006
Strunz 8th edition ID:7/C.21-40
Nickel-Strunz 10th (pending) edition ID:8.CA.65

8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H2O
A : With small and large/medium cations
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Type Occurrence of Gengenbachite

Type Locality:Silberbrünnle Mine, Haigerach valley, Gengenbach, Black Forest, Baden-Württemberg, Germany
Associated Minerals at type locality:
QuartzPyriteJarositeHaigerachiteGypsum
Diadochite

Physical Properties of Gengenbachite

Lustre:Vitreous
Diaphaneity (Transparency):Translucent
Colour:Pale brown
Streak:White
Hardness (Mohs):2
Hardness Data:Estimated
Tenacity:Brittle
Cleavage:None Observed
Fracture:Irregular/Uneven
Density (measured):2.4(5) g/cm3
Density (calculated):2.43(2) g/cm3

Crystallography of Gengenbachite

Crystal System:Trigonal
Class (H-M):3m - Ditrigonal Pyramidal
Space Group:P3 1c
Cell Parameters:a = 9.12(1) Å, c = 16.84(2) Å
Ratio:a:c = 1 : 1.846
Unit Cell Volume:V 1,213.00 ų (Calculated from Unit Cell)
Z:2
Morphology:Simple hexagonal prisms.
X-Ray Powder Diffraction:
d-spacingIntensity
7.89(4)
7.16(10)
4.57(7)
3.57(5)
3.23(6)
3.09(8)
2.87(4)
2.81(5)

Optical Data of Gengenbachite

Type:Uniaxial (+)
RI values: nω = 1.592() nε = 1.596(2)
Maximum Birefringence:δ = 0.004

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Moderate
Optical Extinction:Anomalous pale brownish interference colours.

Chemical Properties of Gengenbachite

Formula:
KFe
3+
3
(HPO
 
4
)
 
4
(H
 
2
PO
 
4
)
 
2
 · 6H
 
2
O
Essential elements:Fe, H, K, O, P
All elements listed in formula:Fe, H, K, O, P
Analytical Data:Part of K+ may be replaced by H3O+.
Relationship of Gengenbachite to other Species
Related Minerals - Nickel-Strunz Grouping):

- + 
8.CA.05Fransoletite
Ca
 
3
Be
 
2
(PO
 
4
)
 
2
(HPO
 
4
)
 
2
 · 4H
 
2
O
8.CA.05Parafransoletite
Ca
 
3
Be
 
2
(PO
 
4
)
 
2
(HPO
 
4
)
 
2
 · 4H
 
2
O
8.CA.10Ehrleite
Ca
 
4
Be
 
3
Zn
 
2
(PO
 
4
)
 
6
 · 9H
 
2
O
8.CA.15Faheyite
(Mn,Mg,Na)Be
 
2
Fe
 
2
(PO
 
4
)
 
4
 · 6H
 
2
O
8.CA.20Gainesite
Na(Na,K)(Be,Li)Zr
 
2
(PO
 
4
)
 
4
 · 1.5-2H
 
2
O
8.CA.20Mccrillisite
NaCs(Be,Li)Zr
 
2
(PO
 
4
)
 
4
 · 1-2H
 
2
O
8.CA.20Selwynite
NaK(Be,Al)Zr
 
2
(PO
 
4
)
 
4
 · 2H
 
2
O
8.CA.25Pahasapaite
Li
 
8
(Ca,Li,K)
 
10.5
Be
 
24
(PO
 
4
)
 
24
 · 38H
 
2
O
8.CA.30Hopeite
Zn
 
3
(PO
 
4
)
 
2
 · 4H
 
2
O
8.CA.35Warikahnite
Zn
 
3
(AsO
 
4
)
 
2
 · 2H
 
2
O
8.CA.40Phosphophyllite
Zn
 
2
Fe(PO
 
4
)
 
2
 · 4H
 
2
O
8.CA.45Parascholzite
CaZn
 
2
(PO
 
4
)
 
2
 · 2H
 
2
O
8.CA.45Scholzite
CaZn
 
2
(PO
 
4
)
 
2
 · 2H
 
2
O
8.CA.50Keyite
Cu
2+
3
Zn
 
4
Cd
 
2
(AsO
 
4
)
 
6
 · 2H
 
2
O
8.CA.55Pushcharovskite
K
 
0.6
Cu
 
18
(AsO
 
4
)(HAsO
 
4
)
 
10
(H
 
2
AsO
 
4
)
 
4
(OH)
 
9.6
·18.6H
 
2
O
8.CA.60Prosperite
CaZn
 
2
(AsO
 
4
)(HAsO
 
4
)(OH)
8.CA.70Parahopeite
Zn
 
3
(PO
 
4
)
 
2
 · 4H
 
2
O
Other Names for Gengenbachite
Synonyms:
IMA2001-003bUnnamed (K-Fe-H Phosphate)
Other Languages:
German:Gengenbachit
Other Information
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 Gengenbachite
Reference List:

- + 
Anisimova, N., Chudinova, N. & Serafin, M. (1997): Preparation and crystal structure of potassium iron hydrogen phosphate KFe3(HPO4)2(H2PO4)6.4H2O. Zeitschrift für Anorganische und Allgemeine Chemie 623, 1708-1714.



Walenta, K. (1998): Neue Mineralfunde aus dem Schwarzwald. 7. Folge, 2. Teil. Lapis, 23(12), 43-48.



Walenta K. & Theye, T. (2004): KFe3+3[(H2PO4)2|(HPO4)4]•6H2O, ein zweites neues Phosphatmineral von der Grube Silberbrünnle im mittleren Schwarzwald. Der Erzgräber, 18(1), 17-23. (in German) [abstracted in Am. Mineral. 90, 1228(2005)]



Walenta, K., Theye, T. & Hatert, F. (2007): Gengenbachit, KFe3+3(H2PO4)2(HPO4)4•6H2O, ein zweites neues Phosphatmineral von der Grube Silberbrünnle im mittleren Schwarzwald, nunmehr eine anerkannte neue Mineralart. Aufschluss, 58, 125-128. (in German)



WALENTA, K. und THEYE, Th. (2009): H-reicher Gengenbachit von der Grube Silberbrünnle bei Gengenbach im mittleren Schwarzwald: Eine neue Mineralart oder nur eine Varietät ? Erzgräber 23, 37-40 (in German). 
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    • Localities for Gengenbachite
    
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
     
    

    • Baden-Württemberg
    

      • Black Forest
    

        • Gengenbach
    

          • Haigerach valley
    
    		Walenta K. & Theye, T. (2004): KFe3+3[(H2PO4)2|(HPO4)4]•6H2O, ein zweites neues Phosphatmineral von der Grube Silberbrünnle im mittleren Schwarzwald. Der Erzgräber, 18(1), 17-23.
    

    


    

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