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Strengite

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Formula:
FePO
 
4
· 2H
 
2
O
System:OrthorhombicColour:Purple, violet, pink, ...
Hardness:3½ - 4
Member of:Variscite Group
Name:Named after Johann August Streng (1830-1897), Professor of Mineralogy, University of Giessen, Germany.

Classification of Strengite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:7/C.09-60
Nickel-Strunz 10th (pending) edition ID:8.CD.10

8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H2O
D : With only medium-sized cations, RO4:H2O = 1:2
Dana 8th edition ID:40.4.1.2

40 : HYDRATED NORMAL PHOSPHATES,ARSENATES AND VANADATES
4 : (AB)5(XO4)2·xH2O
Hey's CIM Ref.:19.13.2

19 : Phosphates
13 : Phosphates of Fe alone
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Type Occurrence of Strengite

Type Locality:Eleonore Mine, Rodheim-Bieber, Wetzlar, Hesse, Germany
Year of Discovery:1877

Occurrences of Strengite

Geological Setting:Secondary mineral formed under surface or near-surface conditions by the alteration of iron-bearing phosphates, such as Triphylite in pegmatite, or Dufrenite, or may occur in limonite ore deposits and gossans, magnetite iron ores, or rarely as a cave mineral.

Physical Properties of Strengite

Lustre:Vitreous
Diaphaneity (Transparency):Transparent, Translucent
Colour:Purple, violet, pink, peach-blossom-red, carmine, greenish white, colorless; Colourless to pale pink in transmitted light.
Streak:white
Hardness (Mohs):3½ - 4
Cleavage:Distinct/Good
Good on {010}, poor on {001}
Density (measured):2.84 - 2.87 g/cm3
Density (calculated):2.84 g/cm3

Crystallography of Strengite

Crystal System:Orthorhombic
Class (H-M):mmm (2/m 2/m 2/m) - Dipyramidal
Space Group:Pbca
Cell Parameters:a = 8.7233(7) Å, b = 9.886(1) Å, c = 10.122(1) Å
Ratio:a:b:c = 0.882 : 1 : 1.024
Unit Cell Volume:V 872.91 ų
Z:8
Morphology:Crystals octahedral {111}; thick to thin tabular {001}; stout prismatic [100] or [010]. May be lathlike, radial fibrous, botyroidal or spherical aggregates and crusts.
Twinning:Rarely on {201}
Crystal Atlas:
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Strengite no.1 - Goldschmidt (1913-1926)
Strengite no.3 - Goldschmidt (1913-1926)

About Crystal Atlas

The mindat.org Crystal Atlas allows you to view a selection of crystal drawings of real and idealised crystal forms for this mineral and, in certain cases, 3d rotating crystal objects. The 3d models and HTML5 code are kindly provided by www.smorf.nl.

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Optical Data of Strengite

Type:Biaxial (+)
RI values: nα = 1.697 - 1.708 nβ = 1.708 - 1.719 nγ = 1.741 - 1.745
2V:Calculated: 72° to 88°
Maximum Birefringence:δ = 0.044

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:High
Dispersion:relatively strong r < v

Chemical Properties of Strengite

Formula:
FePO
 
4
· 2H
 
2
O
Simplified for copy/paste:FePO4·2H2O
Essential elements:Fe, H, O, P
All elements listed in formula:Fe, H, O, P
Common Impurities:Al

Relationship of Strengite to other Species

Series:Forms a series with Variscite (see here)
Forms a series with Scorodite (see here)
Member of:Variscite Group
Other Members of Group:

- +
Mansfieldite
AlAsO
 
4
· 2H
 
2
O
Scorodite
FeAsO
 
4
· 2H
 
2
O
Variscite
AlPO
 
4
· 2H
 
2
O
Yanomamite
InAsO
 
4
· 2H
 
2
O
Common Associates:
VivianiteRockbridgeitePhosphosideriteLimoniteFrondelite
DufréniteCacoxeniteBerauniteApatite
Related Minerals - Nickel-Strunz Grouping):

- +
8.CD.05Kolbeckite
ScPO
 
4
· 2H
 
2
O
8.CD.05Metavariscite
AlPO
 
4
· 2H
 
2
O
8.CD.05Phosphosiderite
FePO
 
4
· 2H
 
2
O
8.CD.05UM2005-02-AsO:AlHPScSi
ScAsO
 
4
· 2H
 
2
O
8.CD.10Mansfieldite
AlAsO
 
4
· 2H
 
2
O
8.CD.10Scorodite
FeAsO
 
4
· 2H
 
2
O
8.CD.10Variscite
AlPO
 
4
· 2H
 
2
O
8.CD.10Yanomamite
InAsO
 
4
· 2H
 
2
O
8.CD.15Parascorodite
FeAsO
 
4
· 2H
 
2
O
8.CD.20Ludlamite
(Fe,Mn,Mg)
 
3
(PO
 
4
)
 
2
· 4H
 
2
O
8.CD.25Sterlinghillite
Mn
 
3
(AsO
 
4
)
 
2
· 4H
 
2
O
8.CD.30Rollandite
Cu
 
3
(AsO
 
4
)
 
2
· 4H
 
2
O
Related Minerals - Hey's Index Grouping:

- +
19.13.1Barbosalite
Fe
2+
 
Fe
3+
2
(PO
 
4
)
 
2
(OH)
 
2
19.13.3Phosphosiderite
FePO
 
4
· 2H
 
2
O
19.13.4Dufrénite
Ca
 
0.5
Fe
2+
 
Fe
3+
5
(PO
 
4
)
 
4
(OH)
 
6
· 2H
 
2
O
19.13.5Giniite
Fe
2+
 
Fe
3+
4
(PO
 
4
)
 
3
(OH)
 
5
· 2H
 
2
O
19.13.6Whitmoreite
Fe
2+
 
Fe
3+
2
(PO
 
4
)
 
2
(OH)
 
2
· 4H
 
2
O
19.13.7Tinticite
Fe
3+
5.34
(PO
 
4
)
 
3.62
(VO
 
4
)
 
0.38
(OH)
 
4
· 6.7H
 
2
O
19.13.8Ferristrunzite
Fe
3+
 
Fe
3+
2
(PO
 
4
)
 
2
(OH)
 
3
· 5H
 
2
O
19.13.9Ferrostrunzite
Fe
2+
 
Fe
3+
2
(PO
 
4
)
 
2
(OH)
 
2
· 6H
 
2
O
19.13.10Beraunite
Fe
2+
 
Fe
3+
5
(PO
 
4
)
 
4
(OH)
 
5
· 6H
 
2
O
19.13.11Vivianite
Fe
2+
3
(PO
 
4
)
 
2
· 8H
 
2
O
19.13.12Metavivianite
Fe
2+
 
Fe
3+
2
(PO
 
4
)
 
2
(OH)
 
2
· 6H
 
2
O

Other Names for Strengite

Other Languages:
German:Strengit
Russian:Штренгит
Simplified Chinese:红磷铁矿
Spanish:Strengita
Traditional Chinese:紅磷鐵礦
Varieties:
Aluminian Strengite

Other Information

Other Information:Soluble in HCl but not in HNO3.
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 Strengite

Reference List:

- +
Zepharovich (1867) Konigliche Akademie der Wissenschaften, Vienna, Sitzber.: 56: 20 (as Barrandite).

Nies (1877) Neues Jahrbuch für Mineralogie, Geologie und Paleontologie, Heidelberg, Stuttgart: 8-16.

Schaller, Waldemar Theodore (1913), The refractive indices of strengite: Journal of the Washington Academy of Science: 3: 249.

Laubmann and Steinmetz (1920) Zeitschrift für Kristallographie, Mineralogie und Petrographie, Leipzig: 55: 542-546.

Goldschmidt, V. (1922) Atlas der Krystallformen. 9 volumes, atlas, and text: vol. 8: 89.

de Jesus (1935) Com. Serv. Geol. Portugal: 19: 65.

Himmel and Schroeder (1935) Zentralblatt Mineralien: 289.

Kokkoros (1938) Prakt. Ac. Athénes: 13: 337 (Min. Abs. (1941): 8: 140).

McConnell (1940) American Mineralogist: 25: 719.

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.: 756-761.

Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (2000) Handbook of Mineralogy, Volume IV. Arsenates, Phosphates, Vanadates. Mineral Data Publishing, Tucson, AZ, 680pp.: 567.

Song, Y., Zavalij, P. Y., Suzuki, M. & Whittingham, M. S. (2002): New iron(III) phosphate phases: crystal structure and electrochemical and magnetic properties. Inorganic Chemistry 41, 5778-5786.

Taxer, K. and Bartl, H. (2004): On the dimorphy between the variscite and clinovariscite group: refined finestructural relationship of strengite and clinostrengite, Fe(PO4) • 2H2O. Crystal Research and Technology 39, 1080-1088.

Internet Links for Strengite

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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Strengite details from Handbook of Mineralogy (PDF)
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    Localities for Strengite

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